The third volume of the present work is devoted to the study of the content of the war that began, the features of the policies of warring groups and states, as well as the military actions of the parties during the first period of the war. It covers events from Nazi Germany's armed attack on Poland to the outbreak of the Great Patriotic War of the Soviet Union (September 1939. — June 1941 . ). The volume highlights a number of problems that make it possible to understand the deep processes of war, the origin of which is associated with the events of that time. An important place is given to finding out the main reasons for the military defeat of the Anglo-French bloc countries. The volume analyzes the military actions and military art of the armies of a number of imperialist powers, the reasons for the success of Hitler's "lightning war" strategy in the campaigns of the first period. The volume covers the direct preparation of fascist Germany for the attack on the USSR. development of the Barbarossa plan , Expansion and strengthening of the fascist bloc , mobilization of economic resources of this block and other preparations , The general purpose of , to suddenly, at the very beginning of the war, strike at the USSR a blow of maximum power and crush the socialist state in a fleeting war, following the example of the campaigns of the first period in Europe. Volume includes an analysis of the domestic and foreign policy of the Communist Party and the Soviet government in the conditions of the already begun world war.