the Soviet Union
China, Japan and Thailand.
heaven and hell
135 countries took part in the war.
There was no Olympics during World War 2, they were all canceled so no countries participated.
America and UK
The question does not say which theater of war. There were several; Atlantic, European, Mediterranean, Pacific, etc. Some countries participated in some theaters but not in others.
Principally the US Britain & Canada. Oh and the Germans ! & the liberated French.
Yes, Montenegro participated in World War I.
It was occupied by Germany on 15 March 1939.
Russia was one of the few countries that participated in both World War I and World War II. During World War I the Russian army was known as the Cossacks.
the soviet union gotta love freakin study island!