Hitler.
Fidel Castro was a Cuban leader and communist ally of the Soviet Union.
Joseph Stalin
The Germans invaded several other countries and were becoming very discriminative against the Jewish people. Germany invaded the Soviet Union. US was attacked at Pearl Harbour by a German ally, Japan. Those were the reasons those two countries got in the war.
Believed it or not : Germany read about : The German-Soviet Treaty of Friendship, Cooperation and Demarcation
Soviet Union
Japan was a German ally and Japan attacked the U.S. Navy at Pearl Harbor. Navies were a lot more important back then.
Italy, Japan, Finland, Slovakia, Croatia, Hungary, Romania & Bulgaria. Also Vichy France collaborated enough with Germany to be considered an ally of Hitler's. It needs to be remembered that the German-Soviet Non-Aggression Pact, paved the way for Hitler to invade Poland. In 1939, the Soviet Union was for all practical purposes allied with Germany. That only changed when Hitler attacked the USSR.
Both were attacked by the Axis in 1941. Soviet by their former ally Germany and USA by Japan. As a result, UK and Soviet forgot their grudges to fight a common enemy, and UK declared war on Japan in solidarity, simultaneously with USA.
Verbundeter
Romania in the World War II was not invaded by German troops; Romania was an ally of Germany against the Soviet Union invaders (occupation of Basarabia and Northern Bukovina).
Hitler betrayed his ally, the Soviet Union.
Answer this question… Become an ally of the Soviet Union