Germany and Japan
The USSR
Germany , japan, Italy http://www.getpcmemory.com
Germany.
Germany, Japan and Italy...............................
That depends on which war you are asking about and which side you would consider yourself to be on.
Germany was a member of the Axis, and so an enemy of the Allies during World War 1 and World War 2. Today, Germany is the most powerful nation in Europe, a founding member of the European Union, and a strong ally of the US.
Germany was Britain's main enemy.
They were not placed anywhere. Japan was not an enemy in World War I.
The question is unanswerable as asked since it does not define who the "enemy" is.
During WWI, Germany had the biggest fleet of submarines and it was known and feared for its sneaky torpedo attacks on enemy ships.
The Cold War involved the entire world; every country was an actual or potential enemy or friend of either the US or the USSR.