Answer:
The following countries fought in World War I:
Allies:
Belgium
France
Great Britain
Greece
Italy
Japan
Montenegro
Portugal
Romania
Russia
Serbia
Siam (Thailand)
United States
Central Powers:
Austria-Hungary
Bulgaria
Germany
Ottoman Empire
The war began on July 28, 1914, when Austria-Hungary declared war on Serbia. The Allies and the Central Powers were drawn into the war by a series of alliances and treaties. The war ended on November 11, 1918, with the victory of the Allies.
Step-by-step explanation: