There are other factors that happened in 1940, but one most notable is that Americans began to fight with RAF forces, called Eagle Squadrons. Then after them came the Flying Tigers. Not too long after that the United States became engaged in WWII.
Most Americans, needed jobs, working hard for food and water. Need houses. During the war, the United States needed Men and Women alike. Bugs Bunny can be seen on TV asking for war bonds. From rifles to tanks and ships and even the laces on their boots, some one needed to make those things. But I will uses planes as an example.
U.S. needs planes. U.S. people build planes. U.S. money pays U.S. people. Everybody is happy.
This is the same throughout 1940-1970. Remember that Detroit used to be rich in automobile business. Your school may want you to think that the environmental reform actions were to save mother nature. If that is the case then I will say it was put in place because too much industry was starting to harm the environment such as the use of coal.
The real reason that was put into place is to offshore American energy to weaken the economy.
U.S. needs keyboards, Chinese builds keyboards, US pays Chinese people.
With no way to get any money back, the U.S. is left in debt.
