In recent years, scholars doing research on the anticommunist and social democratic tradition developed an interpretation in which socialist internationalism is portrayed not as opposed to nationalism but instead as complementary. This allowed them to move away from older perspectives and to examine the main features of international cooperation among socialists in a more positive light. Its substantial and convincing contributions notwithstanding, this literature also displays important shortcomings. Not only does it minimize the challenge that nationalism did pose to transnational solidarities; it is also too focused on Europe and therefore overlooks a more serious limit to internationalism, namely a perspective that proclaimed a principle of color‐blind solidarity among all peoples of the world but in practice built a much more limited transnational community of workers either born in Europe or of European descent. This article engages with these historiographical trends and complicates our knowledge of socialist internationalism in the 1920s by exploring a unique and underresearched event, the “World Migration Congress,” held in London in 1926 and jointly organized by the International Federation of Trade Unions and the Labour and Socialist International, the main transnational networks of trade unionists and political parties of the social democratic tradition. Drawing on the idea that international organizations and meetings can be used as “observation points” for studying global history, the article uses the prolegomena to, the preparations for, and the discussions of this congress as a lens to understand the stances of socialist parties and reformist trade unions regarding the question of migration in the 1920s, explaining to what extent, and for what reason, they have changed in comparison with the prewar period. Moreover, it shows that the stances on migration were intertwined in many ways with socialist and labor perspectives on colonialism and condescending views of the “colored peoples” of the world.