The Germans, by a very wide margin. 85% of the US war effort was directed against Germany, until Germany was defeated. The Pacific War was fought on a shoestring, mainly by the US Navy, the Navy's Marine Corps, which grew to six infantry divisions, and about fifteen army infantry divisions. Everything else was against the Germans.
The Italians also killed a very small percentage of those lost, and the French an even smaller number. The Vichy French were a German ally and fought the US for three or four days after the landings in North Africa in November 1942. Nobody really had their heart in it though, and soon the French came over to our side.
See website: Statistics About the Vietnam War.
Neutral
↓yes↓
Yes
38,000 Americans wounded and 12,000 killed or missing
The families of those killed in the war suffered the most.
A total of 415,000 Americans were killed in World War II.
This question is a bit unclear. If you are referring to the Korean war, 36,516 Americans were killed in that war. If you are referring to World War II, 418.500 Americans were killed in that war.
See website: Statistics About the Vietnam War.
Americans were angry German U-boats had Killed U.S. citizens. -APEX ;)
The Americans came in and killed the Germans, until they surrendered. :D
At least 816,000 americans got killed
35 million people were killed in WWII, 18 million were from Russia.
Neutral
second world war, it was the holocaust and the Americans won but many Jews were killed
Military action.
The Soviet Union has most killed.