The Zimmerwald Conference, held in Zimmerwald, Switzerland, from September 5 to 8, 1915, was the first of three international conferences convened by anti-militarist socialists in response to the outbreak of World War I and the resulting virtual collapse of the Second International. Those participating in this and later conferences at Kienthal and Stockholm are known as the Zimmerwald movement. The Zimmerwald Conference began the final unraveling of the coalition within the Second International between revolutionary socialists, known as the "Zimmerwald Left" supporting Vladimir Lenin's line, and reformist socialists.