Even though revolutionaries today are far from all sharing the analysis that capitalism entered into its phase of decline with the outbreak of the First World War, this was not the case for those who had to respond to this war and who participated in the revolutionary uprisings that followed. On the contrary, as shown in this article, the majority of marxists shared this point of view. Similarly, for them, understanding the new historic period was indispensable for reinvigorating the communist programme and the tactics that flowed from it.