Although the World War served to accentuate the sharp differences in ideology and tactics which already existed among the various branches of the socialist movement, it emphasized the official continuity between socialist theory and the application of that theory under stress of war. From the beginning, however, the growth of the Left School, which was committed to efforts towards transforming the war between nations into a war between classes, had most significance. Their prestige was immeasurably increased by the triumph of the Bolsheviks in Russia, and at length the meeting of the Communist International at Moscow in March 1919 completed the disintegration of the Second International. Mr Fainsod, who has made a thorough study of the sources, presents an illuminating account of events both within and without the socialist party.