The document summarizes Lesson 13 which discusses Germany turning east and launching Operation Barbarossa, the invasion of the Soviet Union in June 1941. It describes Hitler deciding to attack the USSR due to regarding it as Germany's greatest threat and seeing an opportunity due to the Red Army's weakness. It provides details on the scale of the invasion, key battles like Stalingrad, and the immense losses suffered by the Soviet Union, which ultimately bore the main force of fighting and defeating Germany. The lesson emphasizes the massive scale and impact of the German-Soviet war on the outcome of World War 2.