The main theaters of war were:
- The Western Front, which stretched from the North Sea to the Swiss border.
- The Eastern Front, which ran from the Baltic Sea to the Black Sea.
- The Italian Front, which was fought between Italy and Austria-Hungary.
- The Balkan Front, which involved fighting between the Ottoman Empire and various Balkan countries.
- The Middle Eastern Front, which saw battles between the Ottoman Empire and the British Empire.
- The African Front, where fighting occurred between German and Allied forces in several African colonies.
- The Asian Front, where the Ottoman Empire and the British Empire clashed in Mesopotamia (present-day Iraq).
- The Pacific Front, where Japan and Germany engaged in naval battles and seized territories in the Pacific.