With this volume the history of the first century of the International reaches its conclusion. Originally I had intended that the trilogy would come to a close with the centenary of the founding of the First International in September 1964. But before I could finish writing the third volume the tragedy of the Communist revolution in Czechoslovakia had played itself out. 'The Spring of Prague' of 1968, having set in motion a process of change from a Communist dictatorship to a Socialist democracy, was followed within a few months by the invasion of the armies of the five Warsaw Pact powers to forestall reformation in Czechoslovakia. Both revolution and counter-revolution were events of the utmost significance for the history of Socialism-the revolution, for showing that it was possible for a Communist system of totalitarian dictatorship to be transformed without resort to force; and the counter-revolution, for showing how the regime in the Soviet Union has remained essentially unaltered since Stalin's death. The invasion of Czechoslovakia brutally called in question any optimistic perspective of development within the Soviet Union itself.