In 1940, Germany tore through Europe using a shocking new tactic called the Blitzkrieg, or "lightning war." German forces launched catastrophic surprise attacks combining massive air power with fast-moving ground units. The tactic worked: by mid-summer, Denmark, Norway, France, Belgium, Luxembourg and The Netherlands had surrendered.
The Battle of Britain
In July 1940, Germany focused its wrath on Britain. First, the German Luftwaffe (air force) attacked the airfields of Britain's Royal Air Force. The next month, Hitler declared a total blockade of Britain to prevent supplies from entering the country. Then, in September 1940, Hitler ordered an all-out bombing campaign against London.
The outlook for Europe darkened on September 27, 1940, when Germany, Italy and Japan signed the Tripartite Act, uniting their forces into the Axis Powers.