The founders of IWUSP were parties that saw neither the reformistSecond International nor the Communist and pro-SovietThird International as alternatives for affiliation. The IWUSP criticized the other two Internationals for what it perceived to be dogmatism, and advocated that more consideration should be given to the particularities of the political situation in each country. It worked for the unification of the Second and Third Internationals. From April 2 to April 5, 1922 a meeting was held in Berlin with delegations from the three different international bodies to discuss a merger, but unity could not be achieved and the Comintern withdrew from the talks.
In Germany on September 24, 1922, the USPD, one of the main components of IWUSP, merged with the Social Democratic Party of Germany (SPD), a member of the Second International. Discouraged by the intransigent position of the Third International, at the joint congress with the Second International held in Hamburg in May 1923 IWUSP merged with it to form the Labour and Socialist International. Some, such as the FPSR, refused to join the new body.
In the 1930s, a similar effort was made to create an international between the reformism of the Second and the Stalinism of the Third, as the London Bureau of left-wing socialist parties. Sometimes called the "Three-and-a-Half International", it involved many of the same parties.
