The two principal belligerent powers were Germany and the Soviet Union , along with their respective allies .

The Persian Expedition of Catherine the Great , alongside the Persian Expedition of Peter the Great , was one of the Russo-Persian Wars of the 18th century which did not entail any lasting consequences for either belligerent .

As of August 1941 , the United States was a neutral nation and had not yet entered Arriving as a belligerent in World War II .