By 1941 The Axis powers, this included Germany and Italy had taken all of Western Europe. Their control had reached as far west as the bay of Biscay on the west coast of France, they reached as far north as Norway and Finland, as far west as the Caspian sea in Russia. The axis also reached as far south as Libya and Egypt in Africa.
The U.S chose to become isolationists: a national policy of abstaining from political or economic relations with other countries. The U.S was so serious about staying out of any war that when the USS Panay was sunk by Japan, they accepted an apology and a $2 million indemnity.
In Asia however there was a different dominant country, Japan. Japan had stayed and watched things go by in Asia for years, they were like a dormant volcano waiting to erupt. They had watched countries like America, England, France and even Holland take islands and turn them to colonies, so why couldn't they do the same thing? Japan was eager to expand its borders, they knew that they could do it, however there was one problem, The U.S. They were currently the dominant country in the southern islands of Asia. With bases situated in Pearl Harbour and the Philippines, Japan had to weaken the American Navy before they could expand. Japan attacked pearl harbour by surprise, thinking that they could put the American Fleet out of action. This would give them a year to expand all they wanted to. Japan first moved west and took Manchuria and parts of China.
The Japanese thought they had the best opportunity to take resources from these countries, they could take petroleum and even other things, and they could use people as workers. They knew that Britain wouldn't be a problem for them