oil
The United States and Mexico.
United States and the Soviet Union
The US Civil war did not involve communists. It was a war between the Northerners (Union) of the United States and the Southerners (the Confederacy)
Before the beginning of the United States involvement in World War Two, a large portion of the United States public did not favor entering into the war. These individuals were called Isolationists and they favored the United States to not involve itself in any foreign wars. Another term for an individual who opposes military action and war is called a pascifist.
In World War 1, The United States did not get involved at first because none of the issues concerned the United States. Besides, The United States had a long history of not getting involved in wars that did not specifically involve the United States. European nations had been fighting for centuries. Let them continue to fight. Also, each European Nation had a specific reason for fighting. The United States had no reason to get involved.
It is the United States, and we need to know which war.
All three involve a predominantly United States army invading a Middle Eastern country. Aside from that, these wars have little in common.
Japan and United States
Which war?
United States Department of War ended in 1949.
United States Department of War was created in 1789.