The first victim of German aggression was Poland. Owing to the technical and tactical superiority of the German Wehrmacht, German armed forces, other countries followed: Denmark and Norway (April-June 1940), Luxembourg, Holland, Belgium, and France (May-June 1940) as well as Yugoslavia and Greece (April-June 1941) were conquered and occupied in rapid succession. Only Great Britain and the Commonwealth continued the struggle against Germany. With the invasion of the Soviet Union on June 22, 1941 (Operation Barbarossa), the merciless war of conquest, pillage and annihilation against the Soviet Union began - Hitler's actual intent. After great initial successes, the Wehrmacht advanced under increasingly difficult conditions as far as Leningrad (September 1941), Moscow (December 1941), and Stalingrad (August 1942).