Trotsky attended the Zimmerwald Conference of anti-war socialists in September 1915 and advocated a middle course between those who, like Martov, would stay within the Second International at any cost and those who, like Lenin, would break with the Second International and form a Third International. The conference adopted the middle line proposed by Trotsky. At first opposed, in the end Lenin voted for Trotsky's resolution to avoid a split among anti-war socialists.