On the eve of World War II the Soviet Union possessed well developed armed forces and a number of experienced military commanders. Many of them had combat and even commanding experience of the World War I, the Russian Civil War, the Civil War in Spain, the Soviet-Japanese conflicts and the Soviet-Finnish war.
However, the combination of circumstances, namely the surprise attack of Hitler, high efficiency of German military machine, the voluntary, or involuntary participation in German war efforts of the most of Europe, occupied, or controlled by Germany did not allow the Red Army to repel the invasion in June 1941. The Soviet military leaders and the Red Army were being forced to solve the problems they were not prepared for. It was a tough schooling for the Red Army officers. However most of them were able to get through all the ordeals with honor and dignity, and they brought their soldiers as liberators to Warsaw, Vienna, Berlin, Prague and other capitals which found themselves under Nazi yoke at different times.
By the end of World War II, the Soviet Union possessed undoubtedly the best Corps of military commanders in the world history. This fact was illustrated by the ultimate triumph of the Red Army over a million-strong Japanese Kwantung Army in August-September 1945 in northern China. This victory put the end to the World War II.