The Manifesto on war, unanimously adopted in 1912 in Basel, had in view precisely that war between England and Germany with their present allies, which indeed broke out in 1914. The Manifesto directly declares that no popular interest can justify such a war, conducted "for the profits of capitalists and the advantages of dynasties" on the basis of the imperialist, predatory policy of the great powers. The Manifesto directly declares that war is dangerous "for governments" (all without exception), notes their fear of "proletarian revolution," points with complete definiteness to the example of the Commune of 1871 and October–December of 1905, that is, to the example of revolution and civil war. Thus, the Basel Manifesto establishes precisely for this war the tactics of revolutionary struggle of workers on an international scale against their own governments, the tactics of proletarian revolution. The Basel Manifesto repeats the words of the Stuttgart Resolution, that in the event of war breaking out, socialists must use the "economic and political crisis" it creates for "accelerating the fall of capitalism," that is, use the difficulties of governments and the indignation of the masses created by the war for socialist revolution.

The policy of social-chauvinists, their justification of war from bourgeois-liberal points of view, their allowance of "defense of the fatherland," voting for credits, entry into ministries and so forth and so forth, is direct betrayal of socialism, explained only, as we shall see below, by the victory of opportunism and national-liberal working-class politics within the majority of European parties.