The Zimmerwald Conference gathered socialist representatives from various countries in September 1915, amid the ongoing devastation of World War I. Held in Zimmerwald, Switzerland, the conference attracted approximately 38 delegates from nations involved in the war, primarily from Germany, France, Russia, and other European nations. Among the prominent attendees were Leon Trotsky, Rosa Luxemburg, and other notable socialist leaders who vehemently opposed the war and sought to outline a clear anti-war stance. Their objective was to advocate for peace, criticize nationalism, and emphasize the importance of international cooperation among the working class.

The conference was significant not only for its strong anti-war sentiment but also for the strategic discussions around the role of socialists in wartime politics. Delegates deliberated on how to address the growing divisions within the socialist movement regarding the war. Some favored supporting their respective national governments, while others, like those at Zimmerwald, pushed for a united anti-war stance. The resulting Zimmerwald Manifesto expressed the necessity for workers to resist the war and affirmed the importance of solidarity across national boundaries.

The impact of this conference extended beyond its immediate outcomes. It marked the beginning of an organized anti-war socialist movement, eventually leading to the formation of the International Socialist Bureau. The Zimmerwald Conference laid the groundwork for subsequent meetings and initiatives aimed at promoting peace and understanding among the divided socialist factions. Notably, it highlighted the differences between the more radical elements of socialism and those who conformed to nationalist agendas during the war, thus influencing socialist movements for years to come.