Operation Barbarossa was the code name for the German invasion of the Soviet Union in the Second World War. The invasion, which started on 22 June 1941, took place over a front of almost 3,000 kilometres. German forces, supported by Romanians, Finns, Italians, Hungarians, Slovaks, and Croats, tried to conquer the big cities (Moscow, Leningrad, Kiev) and the rich oil fields near the Black Sea as fast as possible. Nazi Germany's armed forces comprised of 3.9 million soldiers (including reserves). The armed forces of the Soviet Union totalled 3.2 million soldiers and later 5 million. In terms of scale, number of soldiers, and number of victims, the war between Germany and the Soviet Union between 1941 and 1945 was the biggest war in history. According to the nazi ideology the Soviet Union consisted of ethnic Slavic people (inferior Untermenschen) who were governed by Jewish Bolsheviks. In his book Mein Kampf (1925), Adolf Hitler had already declared that it was Germany's destiny to "rule the east" and bring an end to "Jewish dominance over Russia".