Japan
Russia.
They were mainly Germany , Italy and Japan.
During World War 2, California was part of the United States, so any enemy of the U.S. would, by extension, have been an enemy of California. For example, Italy, Japan, or Germany.
Germany.
Japan
Germany Italy & Japan ( The Axis)
Germany was Britain's main enemy.
They were not placed anywhere. Japan was not an enemy in World War I.
The Cold War involved the entire world; every country was an actual or potential enemy or friend of either the US or the USSR.
The question is unanswerable as asked since it does not define who the "enemy" is.
Germany. lots of countries had that as their enemy in world war 2.;)