The war was fought between Nazi Germany, its allies and Finland, against the Soviet Union. The conflict began on 22 June 1941 with the Operation Barbarossa Offensive, when Axis forces crossed the borders described in the German-Soviet Nonaggression Pact, thereby invading the Soviet Union. The war ended on 9 May 1945, when Germany's armed forces surrendered unconditionally following the Battle of Berlin (also known as Berlin Offensive), a strategic operation executed by the Red Army. The states that provided forces and other resources for the German war effort included the Axis Powers – foremost Romania, Hungary, Italy, pro-Nazi Slovakia, and Croatia. The anti-Soviet Finland, which had fought the Winter War against the Soviet Union, also joined the Offensive. The Wehrmacht forces were also assisted by anti-Communist partisans in places like Western Ukraine, the Baltic states, and later Crimean Tatars. Among the most prominent volunteer army formations was the Spanish Blue Division, sent by Spanish dictator Francisco Franco to keep his ties to the Axis intact. The Soviet Union offered support to the partisans in many Wehrmacht-occupied countries in Central Europe, notably those in Slovakia, Poland and the Kingdom of Yugoslavia. In addition the Polish Armed Forces in the East, particularly the First and Second Polish armies, were armed and trained, and would eventually fight alongside the Red Army. The Free French forces also contributed to the Red Army by formation of GC3 (Groupe de Chasse 3 or 3rd Fighter Group) unit to fulfill the commitment of Charles de Gaulle, leader of the Free French, who thought that it was important for French servicemen to serve on all fronts. British and Commonwealth forces contributed directly to the fighting on the Eastern Front th ough their service in the convoys and training Red Air Force pilots, as well as in provision of early material and intelligence support. The later massive material support of the Lend-Lease by the United States and Canada played a significant part particularly in the logistics of the war. Total number of Soviet and the European German troops.[27] Date German forces Red Army forces June 1941 3,767,000 (900,000 in the west) 2,680,000 (in theater) 5,500,000 (overall) (~700,000 in Far East[28]) June 1942 3,720,000 (80% in the East) 5,313,000 (~700,000 in Far East[28]) July 1943 3,933,000 (63% in the East) 6,724,000 (~700,000 in Far East[28]) June 1944 3,370,000 (62% in the East) 6,425,000 (~700,000 in Far East[28]) Jan. 1945 2,330,000 (60% in the East) 6,532,000 (Soviet build up in Far East accelerated greatly since February[28]) Apr 1945 1,960,000 6,410,000 Main articles: Aufbau Ost (1940) and Lossberg study For nearly two years the border was quiet while Germany conquered Denmark, Norway, France, The Low Countries, and the Balkans. Hitler had always intended to renege on his pact with the Soviet Union, eventually making the decision to invade in the spring of 1941. Hitler believed that the Soviets would quickly capitulate after an overwhelming German offensive and that the war could largely end before the onset of the fierce Russian winter. Some say Joseph Stalin was fearful of war with Germany or just did not expect Germany to start a two-front war, and was reluctant to do anything to provoke Hitler. Others say that Stalin was eager for Germany to be at war with other capitalist countries. Another viewpoint is that Stalin expected war in 1942 (the time when all his preparations would be complete) and stubbornly refused to believe its early arrival.