Answer:
WWI: Allies and Central Powers
WWII: Allied Powers and Axis Powers
Step-by-step explanation:
WWI: Over 30 nations declared war between 1914 and 1918. The majority joined on the side of the Allies, including Serbia, Russia, France, Britain, Italy and the United States. They were opposed by Germany, Austria-Hungary, Bulgaria and the Ottoman Empire, who together formed the Central Powers.
WWII: Countries like America and Britain were part of the Allied powers. Japan and Germany were part of the Axis powers.