World War I Participants

Wars and Battles

In all, 32 nations were listed as combatants in World War I - some in name only, however. The seemingly disproportionate number of Allied nations is misleading. Germany's military and technological might enabled the Central Powers* to fight on nearly even terms for four years.

* NOTE: The Central Powers are indicated by the shaded areas in the table below.

Country	Date	Event
Austria-Hungary	July 28, 1914	Declared war on Serbia
	August 5, 1914	Declared war on Russia
	August 28, 1914	Declared war on Belgium
	March 15, 1916	Declared war on Portugal
Belgium	August 3-4, 1914	Invaded by Germany
Bolivia	April 13, 1917	Broke relations with Germany
Brazil	April 11, 1917	Broke relations with Germany
	October 26, 1917	Declared war on Germany
Bulgaria	October 14, 1915	Declared war on Serbia
	September 1, 1916	Declared war on Romania
China	March 14, 1917	Broke relations with German
	August 14, 1917	Declared war on Germany
	August 14, 1917	Declared war on Austria-Hungary
Costa Rica	September 21, 1917	Broke relations with Germany
	May 23, 1918	Declared war on Germany
Cuba	April 7, 1917	Declared war on Germany
Ecuador	December 8, 1917	Broke relations with Germany
France	August 12, 1914	Declared war on Austria-Hungary
	August 23, 1914	Invaded by Germany
	November 5, 1914	Declared war on Turkey
	October 16, 1915	Declared war on Bulgaria
Germany	August 1, 1914	Declared war on Russia
	August 3, 1914	Declared war on France
	August 4, 1914	Declared war on Belgium
	March 9, 1916	Declared war on Portugal
Great Britain	August 4, 1914	Declared war on Germany
	August 12, 1914	Declared war on Austria-Hungary
	November 5, 1914	Declared war on Turkey
	October 15, 1915	Declared war on Bulgaria
Greece	June 27, 1917	Declared war on Austria-Hungary, Bulgaria, Germany and Turkey
Guatemala	April 23, 1918	Declared war on Germany
Haiti	July 12, 1918	Declared war on Germany
Honduras	July 19, 1918	Declared war on Germany
Italy	May 23, 1915	Declared war on Austria-Hungary
	August 21, 1915	Declared war on Turkey
	October 19, 1915	Declared war on Bulgaria
	August 28, 1916	Declared war on Germany
Japan	August 23, 1914	Declared war on Germany
	August 25, 1914	Declared war on Austria-Hungary
Liberia	August 4, 1914	Declared war on Germany
Montenegro	August 5, 1914	Declared war on Austria-Hungary
	August 8, 1914	Declared war on Germany
	October 15, 1915	Declared war on Bulgaria
Nicaragua	May 8, 1918	Declared war on Germany and Austria-Hungary
Panama	April 7, 1917	Declared war on Germany
	December 10, 1917	Declared war on Austria-Hungary
Peru	October 6, 1917	Broke relations with Germany
Portugal	March 9, 1916	Object of German war declaration
	March 15, 1916	Object of Austro-Hungarian war declaration
Romania	August 27, 1916	Declared war on Austria-Hungary
	May 7, 1918	Surrendered to Central Powers (Treaty of Bucharest)
	November 10, 1918	Resumed hostilities against Central Powers
Russia	November 2, 1914	Declared war on Turkey
	October 19, 1915	Declared war on Bulgaria
San Marino	June 3, 1915	Declared war on Austria-Hungary
Serbia	August 6, 1914	Declared war on Germany
	November 2, 1914	Declared war on Turkey
Siam	July 22, 1917	Declared war on Germany and Austria-Hungary
Turkey	August 30, 1916	Declared war on Romania
	April 23, 1917	Broke relations with the US
United States	April 6, 1917	Declared war on Germany
	December 7, 1917	Declared war on Austria-Hungary
Uruguay	October 7, 1917	Broke relations with Germany

See also World War I Chronology.