World War 1 (1914-1918):
1. Germany and Austria-Hungary (Central Powers)
2. France, Russia, United Kingdom, and United States (Allied Powers)
World War 2 (1939-1945):
1. Germany, Italy, and Japan (Axis Powers)
2. United States, United Kingdom, France, China, and the Soviet Union (Allied Powers)
These countries were among the major participants and played crucial roles in shaping the outcomes of the wars. Many other nations were also involved, either as allies or co-belligerents.