Hitler surprised Europe with his fast and efficient attack on Poland.
on September 28, 1939 Germany and the Soviet Union divided Poland
Hitler thought that an amphibious attack (land and sea) could be won if they had control over air so in the beginning August 1940 Hitler introduce the air force.
The French and the British were taken by surprise when the German went through the forest instead of around, the French troops were trapped.
on April 9, 1940 Hitler resumed the attack on Denmark.
Germany was now in control of Western and Central Europe. this is when Britain turned to the United States for help, but the United States was under a strict policy of isolationism.