So in our Nations best interest we agreed to help them and enter war in Europe against Germany and Italy. Also, on the contrary we would ally up with Russia in WWII. At that time Russia was also fighting the same war against Germany and Italy. The Russians were on the verge of winning against the Germans by fighting them back out of there country that the Germans had invaded. The U.S made a deal to help the Russians in WWII, since in return they would agree after defeating Germany that they would help us fight Japan and in return get land that they had lost in the Russo-Japanese war in 1904.
Idealistically the United States should have entered war with England against Germany and Russia pre WWII. The Germans and Russians were killing millions of there own people and Jew's. The United States was too busy profiting off of weapons and loans from allied countries, while they did not want to waste American lives fighting a war until something happened to our national interest, which was the when Japan attacked the U.S.
A scenario for the same kind of reasons had also caused the United States to join World War I. During the time of World War I, the United States was neutral and did not want to get into a war with Europe. The United States was making money off of both sides of the war by selling war supplies to England and Germany. At that time though, England was receiving about 70%-80% more products including weapons than Germany was. As a result Germany took advantage of their submarines and made a war zone around the British Isles. They warned any neutral vessels to stay out of these war zones because of a possible attack by mistake. President Woodrow Wilson made it clear to the Germans that he would hold strict accountability, and the Germans would be responsible for any loss of life or property of the U.S. Wilson also stated that German submarines must give a warning to merchant ships with passengers aboard before they were going to attack, so that passengers may escape onto life boats.