Although the threat of conflict had loomed since the early 1930s. Germany and the USSR launched a joint war against Poland in September of 1939, which the Soviets followed up with invasions of Finland, Romania, and the Baltic states across the following year.
After Germany crushed France, and determined that it could not easily drive Great Britain from the war, the Wehrmacht turned its attention back to the East. Following the conquests of Greece and Yugolavia in the spring of 1941, Berlin prepared its most ambitious campaign; the destruction of Soviet Russia. The ensuing war would result in a staggering loss of human life, and in the final destruction of the Nazi regime.
The Fight on Land:
On June 22, 1941, the German Wehrmacht and Luftwaffe struck Soviet forces across a wide front along the German-Soviet frontier. Romanian forces attacked into Soviet-occupied Bessarabia on the same day. The Finnish armed forces joined the fight later that week, with Hungarian troops and aircraft entering combat at the beginning of July. By that time, a significant contribution of Italian troops was on its way to the Eastern Front. A Spanish volunteer division would eventually join the fight, along with large formations recruited from Soviet prisoners of war and from the local civilian population of occupied Soviet territories.
The course of the war is far too complicated to detail in this article. Suffice to say that the German enjoyed overwhelming success for the first five months of the war, before weather and stiffening Red Army resistance led to a Soviet victory in the Battle of Moscow. Germany resumed the offensive in 1942, only to suffer a major defeat at Stalingrad. The Battle of Kursk, in 1943, ended the Wehrmacht’s offensive ambitions. 1943, 1944, and 1945 saw the pace of Soviet conquest gradually accelerate, with the monumental offensives of late 1944 shattering the German armed forces. The war turned the Wehrmacht and the Red Army into finely honed fighting machines, while also draining both of equipment and manpower. The Soviets enjoyed the support of Western industry, while the Germans relied on the resources of occupied Europe.