The European theatre of World War II was the main theatre of combat during World War II. It saw heavy fighting across Europe for almost six years, starting with Germany's invasion of Poland on 1 September 1939 and ending with the Western Allies conquering most of Western Europe, the Soviet Union conquering most of Eastern Europe and Germany's unconditional surrender on 8 May 1945. The Allied powers fought the Axis powers on two major fronts as well as in a strategic bombing offensive and in the adjoining Mediterranean and Middle East theatre.