How and why did a catastrophe of unprecedented scale break out - the Second World War, in which 61 states were involved and the victims of which were more than fifty million people? Why did the USSR and Western countries fail to build a collective security system? What are the reasons for the tragedy of the initial period of the Great Patriotic War? These questions, the authors of the book believe, can only be answered in the context of the processes and phenomena that took place in the world in the 1920s – early 1940s, when fascist-militarist forces emerged and united into an aggressive military bloc. The book is based on a broad documentary basis key aspects of the military-political history of the USSR are considered in the context of world events - from the Treaty of Versailles and the Paris Peace Conference to the beginning of the Great Patriotic War.