Labor and Socialist International

The Labour and Socialist International (LSI; German: Sozialistische Arbeiter-Internationale, SAI) was an international organization of socialist and labour parties, active between 1923 and 1940. The group was established through a merger of the rival Vienna International and the former Second International, based in London, and was the forerunner of the present-day Socialist International.

The LSI had a history of rivalry with the Communist International (Comintern), with which it competed over the leadership of the international socialist and labour movement. However, unlike the Comintern, the LSI maintained no direct control over the actions its sections, being constituted as a federation of autonomous national parties.

Despite the hostility expressed by the Communist International, the left wing of the social democratic movement sought an international "union of the whole proletariat" through 1922. This initiative finally came to a close at the end of the year with the convocation of the 4th World Congress of the Comintern, which decisively rejected calls for a broad and inclusive international body.

This rejection by the Communist wing of the international socialist movement left the center and right — in the form of the Vienna International and the London International, respectively — to patch together their own joint international body. Planning for such a body began in January 1923, a month after the conclusion of the Comintern's 4th World Congress, with the Executive Committees of the Vienna and London groups issuing a joint statement condemning the Communists' decision. The two Executive Committees subsequently issued a convention call for a unification congress in May.

On May 21, 1923, some 620 delegates representing 41 socialist political parties in 30 countries was convened in Hamburg, Germany to bring about the unification of the two Internationals. A wide array of political tendencies were represented among these delegates, running the ideological gamut from activists in the left wing of the French Section of the Workers' International (SFIO) and the Independent Social Democratic Party of Germany (USPD) to moderate reformists of the British Labour Party.

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