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The Second International, also called the Socialist International, was a political international of socialist and labour parties and trade unions which existed from 1889 to 1916. It included representatives from most of Europe's major working-class organizations, though was dominated by the Social Democratic Party of Germany. The organization continued the work of the First International, which had been dissolved in 1876, and was ideologically dominated by Marxism, although other viewpoints were represented, most notably anarchism until anarchists were expelled in 1893. Its key thinkers included Friedrich Engels, Karl Kautsky, and Georgi Plekhanov, with the ideas of Vladimir Lenin and Rosa Luxemburg also being influential.

The Second International was primarily concerned with developing and coordinating strategy and tactics, and with establishing common policies for its member parties. Congress meetings were held every two to four years, and an International Socialist Bureau administered and coordinated its affairs. On the issue of socialist cooperation with bourgeois governments, the international deemed it permissible as a temporary expedient. The question of reform or revolution to achieve communism resolved against revisionist thinker Eduard Bernstein, who argued for a gradualist and electoralist strategy. On colonialism, the international deemed that it was never a progressive force. The international's position on war was to prevent it, and if it broke out to exploit it to bring about the collapse of capitalism. However, the outbreak of World War I in 1914 saw the international split into pro-Allied, pro-Central Powers, and antimilitarist factions and cease to function by 1916. After the war, the remaining factions of the international went on to found the Communist International, International Working Union of Socialist Parties, and Labour and Socialist International.^[1]

The foundation of a new international was first discussed at a conference at Chur in October 1881. Delegates included members of the Social Democratic Party of Germany (SPD), Belgian socialists, the Federation of the Socialist Workers of France (FTSF), French and German-speaking Swiss delegations, two Polish delegates, and one delegate each for Russia and Hungary. The conference did not form an international that year, but decided to write a new socialist manifesto to be approved at a subsequent meeting.^[2] According to Yuri Steklov, the conference was exceedingly poorly organized, and thus didn't engender confidence that a new international could be founded.^[3]

Efforts to found a new international were greatly complicated by a factional divide within the FTSF between the Marxists and Possibilists. From its founding in 1879, a faction inspired (though not always endorsed) by Paul Brousse had moved away from revolutionary socialism towards a more reformist approach, arguing that socialists should pursue whichever reforms are "possible" at any given time, while still taking advantage of revolutionary opportunities.^[4] A Marxist faction led by Jules Guesde and Paul Lafargue, and supported by Karl Marx and Friedrich Engels, denounced the possibilist faction as opportunists, founding the rival French Workers' Party in 1882. Confusingly, both parties would call themselves the Parti Ouvrier (worker's party), and so were generally known as the Marxist party and Possibilist party.^[5]

The Possibilist party would convene international socialist conferences several times, in 1883, 1884, and 1886. At the 1886 convention, it was decided that another convention would be held in 1889, but the Social Democratic Party of Germany disagreed with the decision, and the decisions at the 1886 convention were generally seen to have lacked legitimacy. The SPD held its own convention in St. Gallen in 1887, whereupon the FTSF decided to hold their own international conference the following year. When the London International Trades Union Congress declared that a new international meeting would be called in Paris in 1889, both the SPD and Possibilists decided to fold their next congress into the new one, creating one large international meeting. However, the SPD had only joined the new meeting on the condition that the hosts would not ask for records and names from the delegates, since the SPD could have faced immediate dissolution and ejection from the Reichstag if the German government discovered it had sent delegates abroad. When the Trade Union Congress responded that delegates would only be considered legitimate if they could prove their mandate with appropriate records, the SPD and their Marxist supporters decided to hold a separate congress near the Possibilist congress, with the hope of uniting the two at a later date. The separation into two congresses in 1889 effectively forced foreign delegations to divide themselves up between supporters of the Possibilists, and supporters of the SPD.^[5]

When the first meetings of the new international were held in Paris on 14 July 1889, the two factions were still discussing the possibility of unity. The two meetings had effectively divided the entire European socialist movement into two camps: the Possibilists, supported by the British Social Democratic Federation, and the Marxists, supported by the SPD, the British Socialist League, and most of the other European delegates. The Possibilists insisted upon recording the names and documentation of delegates so as to verify their mandate, while the Marxists (many of whom faced conditions of illegality at home) were concerned about information being discovered by the authorities.^[6] However, according to John Burns, William Morris, and some of the Marxist delegates, there were no real concerns around verification until Henry Hyndman proposed the measure, and the dispute was a deliberate ploy to split the congress in two, an allegation strongly rebuked by Annie Besant.^[7][8][9] Regardless of which account is true, the split between the Possibilists and Marxists threatened to create two separate internationals, with subsequent conferences in Brussels and Zürich respectively. However, after the anger aroused during the split congresses had died down, the Marxists ultimately agreed to join the Brussels conference and create a single, unified international.^[2]

While the factional divide between the Possibilists and Marxists abated to a degree, the international continued to be plagued by major factional disputes at each congress. By the time of the 1896 congress in London, considered "the most agitated, the most tumultuous, and the most chaotic of all the congresses of the Second International",^[10] a more concrete rift had developed between reformist and revolutionary approaches to socialist power, which resulted in many factions along national lines.^[2]

Among the Second International's famous actions were its 1889 declaration of 1 May (May Day) as International Workers' Day and its 1910 declaration of the International Women's Day, first celebrated on 19 March and then on 8 March after the main day of the women's marches in 1917 during the Russian Revolution. It initiated the international campaign for the eight-hour working day.^[11]

The International's permanent executive and information body was the International Socialist Bureau (ISB) based in Brussels and formed after the International's Paris Congress of 1900. Emile Vandervelde and Camille Huysmans of the Belgian Labour Party were its chair and secretary. Vladimir Lenin was a member from 1905.

The pre-war period is notable for the repeated statements against militarism jointly issued by members of the international, which were largely ignored in 1914. At the founding of the international, Paul Lafargue affirmed that socialists were "brothers with a single common enemy [...] private capital, whether it be Prussian, French, or Chinese."^[12] The 1907 conference at Stuttgart resulted in a joint resolution which stated that "struggle against militarism cannot be separated from the Socialist class struggle in general."^[13] The extraordinary congress in Basel in 1912 was largely devoted to a discussion of rising militarism, which resulted in a manifesto stating that the working classes should "exert every effort in order to prevent the outbreak of war by the means they consider most effective."^[14] Finally on July 29, 1914, the ISB held an emergency meeting wherein it “resolved unanimously that it shall be the duty of the workers of all nations concerned not only to continue but to further intensify their demonstrations against the war, for peace, and for the settlement of the Austro-Serbian conflict by international arbitration.”^[2]

The antimilitarist French Section of the Workers' International (SFIO) leader Jean Jaurès's assassination a few days before the beginning of the First World War generated an outpouring of antimilitarist sentiment from many members of the socialist international. Nonetheless, immediately after the outbreak of war, all of the major socialist parties in belligerent nations (with the notable exception of the Independent Labour Party) had issued statements in full support of war. This took many socialist parties in neutral countries by surprise, such as the Romanian Social Democrats, who initially refused to print the SPD's endorsement of war, believing it to be a forgery.^[15]

The war effectively split the international into three factions: the pro-war social democratic parties in the Central Powers, the pro-war parties of the Triple Entente, and the various anti-war parties, including the parties in neutral countries and many pacifist or revolutionary socialist parties. The leadership of the international, especially Secretary General of the ISB Camille Huysmans, attempted to coordinate meetings between the various parties, including one-on-one meetings between pro-war leaders from opposing sides, but by July 1916 the ISB's attempts had failed.^[16]

Despite the failure to bring the various parties together into a single congress, each faction would hold its own conferences during the war. The German, Austrian, and Hungarian pro-war parties successfully met at the Vienna Socialist Conference of 1915.^[17] The pro-war parties in the allied powers successfully met four times at the Inter-Allied Socialist Conferences of World War I.^[18] Anti-war parties first met as representatives from the neutral countries at the Neutral Socialist Conferences during the First World War, then as part of the Zimmerwald movement which successfully convinced the neutral, pacifist and revolutionary parties to split from the international. The Zimmerwald movement would lead to a much greater schism between the reformist and revolutionary wings of the international, which would eventually result in the Third International.^[19]

In July 1920 at Geneva, the last congress of the Second International was held, following its functional collapse during the war. However, some European socialist parties refused to join the reorganised International and decided instead to form the International Working Union of Socialist Parties (IWUSP) (Second and a half International or Two-and-a-half International), heavily influenced by Austromarxism. In 1923, IWUSP and the Second International merged to form the social democratic Labour and Socialist International which continued to exist until 1940. After World War II, a new Socialist International was formed to continue the policies of the Labour and Socialist International, which continues to this day.

Another successor was the Third International organised in 1919 by revolutionary socialists after the October Revolution and the creation of the Soviet Union. It was officially called the Communist International (Comintern) and lasted until 1943 when it was dissolved by then Soviet leader Joseph Stalin.

The Second International had a complex and changeable relationship to anarchist groups and individuals. The conflict between anarchist and Marxist factions dated back to the days of the First International, which was frequently characterized by clashes between the state socialists (ie. the Lassallists, Marxists and Blanquists) on one hand, and the anarchists (ie. the mutualists and collectivists) on the other. Tensions reached their peak after the Hague Congress of 1872, wherein an attempt was made to expel Mikhail Bakunin and James Guillaume and move the general council to New York City, effectively disbanding the organization. Competing anarchist and state socialist internationals attempted to continue on alone, but both ultimately ended in failure within five years.^[20][21][22]

As a result of the 1872 split, anarchist and social democratic factions were reluctant to work with one another. The anarchist organizations ultimately refused to participate in the Chur congress of 1881, instead opting to hold a separate congress in London which would result in the International Working People's Association or "black" international. As a result, anarchist organizations were not involved in discussions to found the Second International in 1889. Nonetheless, several anarchist individuals would hold positions in the international, and anarchists were actually the dominant faction within several of the ostensibly Marxist organizations, such as the Social Democratic League.^[23] Despite holding positions as delegates, and ostensibly being welcome during the first two congresses, expressions of anarchist ideas were often shouted down, and in one incident Francesco Saverio Merlino faced violence from the other delegates, but was shielded by delegates from the British Socialist League.^[24][25]

Anarchist individuals and factions would ultimately be officially excluded at the 1893 Zurich congress, prompting many social democratic parties to expel their anarchist factions. An attempt to repeal the decision was made at the subsequent London congress of 1896, which was attended by anarchist figures like Errico Malatesta and Christiaan Cornelissen, supported by some Marxist figures including Keir Hardie, Tom Mann, and a very sickly William Morris.^[26] Discussion of anarchism would dominate the congress, but the anarchists were not successful in reversing their expulsion.^[26]

Bolshevik figures like Vladimir Lenin and Nikolai Bukharin gained international notability during the war years for their criticisms of the international's inability to coordinate an anti-war opposition. Lenin and Bukharin based their critique in a theory of imperialism, associating the reformism and social imperialism of the various pro-war parties with the rise of monopoly capital and imperialist superprofits. The Bolsheviks believed that monopoly capitalists had created large national blocs of capital which sought to divide the world among themselves, a process which created superprofits either through tariffs, or as a side-effect of capital export. Superprofits extracted from colonized areas were diverted to the advanced countries, whereupon a portion was given over to a labor aristocracy as a "bribe", in the form of higher wages. The Bolsheviks saw this privileged, highly-skilled strata of workers organized into craft unions as a threat within the labor movement, which would try to take leadership positions in order to gain higher wages at the expense of other proletarians. Lenin and Bukharin believed that the leadership of the international, especially in the pro-war parties, were largely labor aristocrats or else were influenced by a labor aristocratic ideology.^[27][28]

While the labor aristocracy thesis informed the Bolsheviks' general critique of the international, Lenin also had more specific criticisms of the leaders of the international who had sided with the pro-war parties. Lenin believed that there were really two pro-war ideologies in the international, the "who started it?" theorists represented by Georgi Plekhanov, and the more nuanced "saccharo-conciliatory chauvinis[ts]" represented by Karl Kautsky. Plekhanov generally agreed with the Entente, believing that German warmongering was a criminal act that needed to be punished by an international coalition. Kautsky suggested that the principle of national self-determination gave each national proletariat the right to defend itself, including violence against other proletarians. Lenin believed that both positions represented different attempts to rationalize labor aristocratic ideology.^[29]

Despite issuing a statement against colonialism at the 1896 London congress,^[2] the international was criticized by anti-colonial figures for providing insufficient opposition to colonial expansion. While the pre-war international was relatively consistent in its opposition to an inter-imperialist conflict between European powers, it was often paternalistic towards colonial areas, and statements often mentioned a need to educate or civilize conquered peoples. By the Stuttgart congress of 1907, parties in the international had substantially shifted away from their earlier consensus on ostensible anticolonialism towards a mix of overtly pro-colonial, anti-colonial and neutral views. These divisions were made apparent in a proposal by the Dutch delegate Henri van Kol that the international drop its anticolonial position, which was defeated 128 votes to 108.^[30] Part of this was due to a concerted effort by non-socialist parties and the media to question the patriotism of anti-colonial parties, for example the SPD and Catholic Centre Party of Germany initially opposed the Herero and Namaqua genocide before giving in to extreme political pressure. The Dutch Social Democratic Workers' Party was particularly insistent on the legitimacy of a "socialist colonialism", and opposed most anti-colonial resolutions on the basis that colonialism under a socialist government could be benevolent and mutually beneficial. The French SFIO likewise supported a policy of "national colonialism", while the right wing of the SPD supported "national imperialism", and the British Labour Party's stated policy was "ethical imperialism".^[31] Ho Chi Minh wrote that the Second International's pro-colonial reputation led him to support the Third International instead.^[32]

From its outset, one of the objectives of the international was to build a consensus on the "Jewish question", a contemporary term for debates on the civil, legal, national, and political status and treatment of Jews as a minority group. The founders of the international in 1889 included some noted antisemites including Henry Hyndman, who led the English attendees at the Possibilist congress, but also a great many Jewish-led organizations and Jewish delegates.^[33][34]

Despite these differences, at the 1891 congress in Brussels the delegates managed to pass a unanimous resolution against antisemitism; however, at the insistence of the Blanquist delegates Dr. A. Regnard and M. Argyriades, the congress would pass an amended resolution targeting "philo-semitic tyranny", noting that many Jewish bankers were "great oppressors of labour". Regnard stated that he believed many Jews owned the newspapers, while Argyriades stated his belief that Jews owned the banks and many industries. The Times reported that the pair's amendment was greeted with applause and was passed with only minor opposition.^[35] This has been noted as a major instance of antisemitism within the international, as although all of the delegates were ostensibly opposed to antisemitism, the resolution indicates that many delegates believed in the antisemitic canard that Jews controlled the banking system, or that financial capital was somehow intrinsically tied to Jews. In addition to antisemitism against Jewish bankers and capitalists, the British socialist newspaper Justice reported that "[t]here appears to be a strong feeling against the Jews in the Congress."^[36]

The "Jewish question" was not revisited after the 1891 congress; however, after the establishment of the ISB there appears to have been some attempt to rectify the imbalance against Jewish organizations within the international by granting them additional consultative votes on relevant issues. Such votes were granted to the Jewish Socialist Workers Party and Zionist Socialist Workers Party at the 1907 congress.^[37][38]

• International Socialist Bureau (1900–1916): The BSI was the only permanent organizing committee of the international, founded to provide a degree of continuity between conferences. It met yearly alongside the regular conferences to coordinate decision-making between the member parties. After 1914 the BSI failed to meet aside from sporadic attempts at one-on-one meetings between delegates, contributing to the dissolution of the international.^[39]
• International Federation of Socialist Young People's Organizations (1907–1916): Socialist youth groups were common among member parties of the international from its foundation, and the need to create youth organizations was encouraged at the 1900 and 1904 conferences.^[40] At the 1907 Stuttgart conference a youth federation was officially formed, with a headquarters in Vienna.^[41][42] This organization actually outlasted the international as the International Union of Socialist Youth.^[43]
• Women's International Council of Socialist and Labour Organizations (1907–1916): The women's international was formed out of the International Socialist Women's Conferences held in conjunction with the regular congresses of 1907, 1910, and 1915. Clara Zetkin was elected as secretary of the organization, with Die Gleichheit chosen as the official newspaper. The women's grouping outlasted the international as Socialist International Women.^{[44][45][46][47]}

	Party	State	Member from	Notes
	Armenian Revolutionary Federation	Ottoman Empire, Russian Empire, Qajar Iran (Armenian)	1907–1916
	Australian Socialist League	Colony of New South Wales	1893–1901
	Battersea Labour League	United Kingdom	1891–1900	Present in 1891, later became part of the Labour Party.[48]
	Belgian Labour Party	Belgium	1889–1916	Founding member.
	Bloomsbury Socialist Society	United Kingdom	1889–1900	Founding member. Later became part of the Labour Party.[48]
	Bulgarian Workers' Social Democratic Party	Bulgaria	1893–1903
	Bulgarian Social Democratic Workers Party (Broad Socialists)	Bulgaria	1903–1916
	Bulgarian Social Democratic Workers' Party (Narrow Socialists)	Bulgaria	1903–1915
	Central Revolutionary Committee	France	–1898
	Czechoslavonic Social Democratic Workers' Party	Austria-Hungary (Czechoslovak)
	Democratic Socialist Party of Basle	Switzerland	1891	Present at the 1891 congress. Membership is unclear after 1891.
	Democratic Socialist Party of St. Gall	Switzerland	1891	Present at the 1891 congress. Membership is unclear after 1891.
	Dublin Socialist Club	United Kingdom (Irish)	1889–1896	Founding member.[7]
	Emancipation of Labour	Russian Empire	1889–1903	Founding member. Would go on to become the Russian Social Democratic Labour Party and is sometimes referred to as such.
	Fabian Society	United Kingdom	1889–1896	Founding member. Membership is unclear after 1896.[7]
	Federation of the Socialist Workers of France	France	1889–1902	Founding member. Sometimes confusingly referred to as the Parti Ouvrier.
	French Section of the Workers' International	France	1905–1916	Founded as a project of the international to merge the French parties.
	French Socialist Party (1902)	France	1902–1905	Ordered by the international to merge into the French Section of the Workers' International.
	French Workers' Party	France	1889–1902	Founding member. Otherwise known as the Parti Ouvrier, not to be confused with the Federation of the Socialist Workers of France from which it split.
	General Jewish Labour Bund in Lithuania, Poland and Russia	Russian Empire	1897–1912
	General Workers Party of Hungary	Austria-Hungary (Hungarian)	1889–1890	Founding member.
	German Workers Union of New York	United States (German)	1889	Founding member and trade union. Membership is unclear after 1889.
	Grütli Union	Switzerland	1889–1916	Founding member.
	Independent Labour Party	United Kingdom	1893–1916
	International Typographical Union	United States	1889	Founding member and trade union. Membership is unclear after 1889.[7]
	Italian Socialist Party	Kingdom of Italy	1892–1914
	Italian Workers' Party	Kingdom of Italy	1889–1892	Founding member.
	Jewish Social Democratic Labour Party in Palestine (Poale Zion)	Ottoman Empire (Jewish-Palestinian)	1915–1916
	Jewish Socialist Workers Party	Russian Empire (Jewish)	1907–1916	The JSWP was incorporated as a sub-group of the Socialist Revolutionary Party in 1907, but had a separate consultative vote in the Stuttgart congress.[37][38]
	Knights of Labor	United States	1889	Founding member. Membership is unclear after 1889.
	Knights of Labour, Birmingham	United Kingdom	1889	Founding member. Membership is unclear after 1889. A separate British entity to the Knights of Labor.[7]
	Norwegian Labour Party	Norway
	Labour Party of Portugal	Portugal	1889	Founding member. Membership is unclear after 1889. May refer to the Portuguese Socialist Party.
	Legal Eight Hours and International Labour League	United Kingdom	1891–1900	Present in 1891, later became part of the Labour Party.
	Luxembourg Socialist Workers' Party	Luxembourg	1902–1916
	Metropolitan Radical Federation	United Kingdom	1889	Founding member. Membership is unclear after 1889.[7]
	Miners' Federation of Great Britain	United Kingdom	1896–	Trade union.
	National Union of Gas Workers and General Labourers	United Kingdom	1889–1891	Founding member. Membership is unclear after 1891. Initially called the Gas Stoker's Union, gas workers were a very important force behind the 8 hour day.[7][48]
	Paris Indian Society	British Raj	1907	While not a party as such, the Paris Indian Society represented Indian nationalist interests at the 1907 congress.
	Poale Zion	Multiple states.		A very loose Marxist-Zionist movement starting in 1903.
	Polish Social Democratic Party of Galicia	Austria-Hungary (Polish-Ukrainian)	1890–1916
	Polish Social Revolutionaries	Russian Empire (Polish)	1891	Minor party present in 1891, later membership is unclear.
	Polish Socialist Party	Russian Empire (Polish)	1893–1916
	Republican Socialist Union of Alsace-Lorraine	German Empire	1889	Founding member. Membership is unclear after 1889.
	Revolutionary Communist Alliance	France	1896–1901
	Revolutionary Socialist Workers' Party	France	1890–1901
	Russian Social Democratic Labour Party	Russian Empire	1898–1912	Delegates began acting independently of the party from 1900, which intensified after the split into the Bolsheviks and Mensheviks from 1903.
	Russian Social Democratic Labour Party (Bolsheviks)	Russian Empire	1912–1916	Actually had separate delegates at the international from 1903 as members of the RSDLP.
	Russian Social Democratic Labour Party (Mensheviks)	Russian Empire	1912–1916	Actually had separate delegates at the international from 1903 as members of the RSDLP.
	Scottish Labour Party	United Kingdom	1889–1895	Founding member.
	Second Proletariat	Russian Empire (Polish)	1889–1893	Founding member.
	Serbian Social Democratic Party	Serbia	1903–1914
	Social Democracy of the Kingdom of Poland and Lithuania	Russian Empire (Polish)	1893–1916
	Social Democrat Hunchakian Party	Russian Empire, Ottoman Empire (Armenian)	1904	Represented by Georgi Plekhanov at the 1904 congress, it is unclear if the party attended other congresses.[49]
	Social Democratic Federation	Denmark
	Social Democratic Federation	United Kingdom	1889–1911	Founding member.
	Social Democratic League	Netherlands	1889–1900	Founding member.
	Social Democratic Workers' Party of Austria	Austria-Hungary (Austrian)
	Social Democratic Party of Bosnia–Herzegovina	Austria-Hungary (Muslim-Serb-Croat)	1909–1916
	Social Democratic Party of Croatia and Slavonia	Austria-Hungary (Croat-Serb)	1894–1916
	Social Democratic Party of Finland	Russian Empire (Finnish)
	Social Democratic Party of Germany	German Empire	1889–1916	Founding member.
	Social Democratic Party of Hungary	Austria-Hungary (Hungarian)	1890–
	Social Democratic Party of Romania	Romania	1910–1916
	Social Democratic Party of Switzerland	Switzerland	1889–1916	Founding member.
	Social Democratic Workers' Party	Netherlands	1894–1916
	Social Democratic Workers' Party of Romania	Romania	1893–1900
	Socialist group of Buenos Aires	Argentina	1889	Founding member. Membership is unclear after 1889 but likely folded into the Socialist Party.
	Socialist Labor Party	Australia	1901–1916
	Socialist Labor Party of America	United States	1889–	Founding member.
	Socialist League	United Kingdom	1889–1901	Founding member.
	Socialist Party	Argentina	1896–1916
	Socialist Party of Denmark	Denmark	1889	Founding member. Membership is unclear after 1889. May refer to the Social Democratic Party of Denmark.
	Socialist Party of Great Britain	United Kingdom	1904	The SPGB attended just one congress of the international in 1904 before splitting to form the World Socialist Movement.
	Socialist Party of Uruguay	Uruguay	1910–1916
	Socialist Party of America	United States	1901–1916
	Socialist Party of France	France	1902–1905	Ordered by the international to merge into the French Section of the Workers' International.
	Socialist Revolutionary Party	Russian Empire	1902–1916
	Socialist Revolutionary Party	France	1898–1901
	Spanish Socialist Workers' Party	Spain
	Swedish Social Democratic Party	Sweden	1889–1916	Founding member.
	Third Proletariat	Russian Empire (Polish)	1900–1909
	United Brothers of Iowa	United States	1889	Founding member. Membership is unclear after 1889.
	United Hebrew Trades	United States (Jewish)	1889–1891	Founding member and trade union. Membership is unclear after 1891.
	Yugoslav Social-Democratic Party	Austria-Hungary (Slovene-Croat)	1898–1916
	Zionist Socialist Workers Party	Russian Empire (Jewish)	1907–1908	The ISB granted the ZSWP a consultative vote in 1907, but the decision was overturned a year later.[37][38]

Source: Julius Braunthal (1980). History of the International: Volume 3, 1943–1968. London. Victor Gollancz. p. 562.

After World War I, there were three Socialist Conferences in Switzerland. These served as a bridge to the creation of the Labour and Socialist International.

Source: Julius Braunthal (1980). History of the International: Volume 3, 1943-1968. London. Victor Gollancz. pp. 562–563.

Chronological list by ideology.

United left wing

• International Workingmen's Association, the First International (1864–1876); various left-wing movements

Anarchist

• International Anarchist Congresses: at first with the First International; followed by:
  • International Working People's Association, sometimes known as the "Black" International (1881-1887); anarchist
  • International Workers' Association – Asociación Internacional de los Trabajadores IWA–AIT (est. 1922) and the International of Anarchist Federations (IFA; est. 1968), with several spin-offs: Libertarian Communist International (est. 1954), Anarchist International Conference (est. 1958), International Libertarian Solidarity (SIL/ILS) network (est. 2001)

Socialist & labour

After the Second International (1889–1916):

• Berne International (est. 1919), socialist
• International Working Union of Socialist Parties (IWUSP), aka 2½ International or Vienna International (1921-1923)
• Labour and Socialist International (1923-1940), created by merger of Vienna and Berne Internationals

Communist

• Communist International, aka Third International or Comintern (1919-1943)

Trotskyist

• Fourth International (1938-1953 schism) led by the International Secretariat (ISFI); followed by Trotskyist internationals.
• Fourth International (post-reunification) (since 1963), by reunification of ISFI and parts of the International Committee of the Fourth International (ICFI)

Democratic socialism

• Socialist International (est. 1951)

Reunification efforts

• Fifth International, phrase referring to socialist and communist groups aspiring to create a new workers' international.

• "The Second International". Marxists.org.
• Igor Mikhailovich Krivoguz. "The Second International 1889-1914: The History and Heritage". Progress Publishers, Moscow, 1989.
• "History of the Second International" (in French and English).
• "German social-democratic party and the Second International". Fractal-vortex.
• Dutt, R. Palme (1922). "International, The" . Encyclopædia Britannica (12th ed.).