In 1940, Hitler began a successful invasion that saw most of Western Europe fall to German forces before the year's end. Hitler's forces occupied much of Western Europe while continuing to bomb Great Britain and preparing to invade Russia.
On May 10, 1940, German troops began their offensive in Belgium, going through Luxembourg on the way to France, which fell on June 14, 1940. Belgium, the Netherlands, Italy, Norway, Denmark and the Vatican became occupied territories along with parts of France. Southern France was left unoccupied, and an ostensibly independent French government was set up in the town of Vichy.
Spain, Portugal, Switzerland and Sweden remained neutral in the conflict throughout 1940. The Germans attempted to gain air superiority over the British Royal Air Force through a campaign of bombing in the southeast, but could not succeed. Believing it essential to Germany's success, Hitler postponed his invasion of Great Britain until 1941. By December 1940, the German invasion of Russia was underway.
In the occupied countries, the German forces made attempts to gain the support of key groups in their respective societies and used propaganda to try to influence the public view of events. However, resistance groups began to form at the same time to work against the occupying forces.