Nations Involved in World War I

COUNTRY

EVENT

DATE

Austro-Hungarian Empire	Declared war on Serbia	July 28, 1914
	Declared war on Russia	August 6, 1914
	Declared war on Belgium	August 28, 1914
	Declared war on Portugal	March 15, 1916
Belgium	Refused German ultimatum demanding permission for German troops to cross Belgium	August 2, 1914
	Invaded by Germany	August 3-4, 1914
Bolivia	Severed relations with Germany	April 13, 1917
Brazil	Severed relations with Germany	April 11, 1917
	Declared war on Germany	October 26, 1917
Bulgaria	Declared war on Serbia	October 14, 1915
	Declared war on Romania	September 1, 1916
China	Severed relations with Germany	March 14, 1917
	Declared war on Germany	August 14, 1917
	Declared war on the Austro-Hungarian Empire	August 14, 1917
Costa Rica	Severed relations with Germany	September 21, 1917
	Declared war on Germany	May 23, 1918
Cuba	Declared war on Germany	April 7, 1917
Ecuador	Severed relations with Germany	December 8, 1917
France	Invaded by Germany	August 2, 1914
	Declared war on the Austro-Hungarian Empire	August 12, 1914
	Declared war on Turkey	November 5, 1914
	Declared war on Bulgaria	October 16, 1915
Germany	Declared war on Russia	August 1, 1914
	Declared war on France	August 3, 1914
	Declared war on Belgium	August 4, 1914
	Declared war on Portugal	March 9, 1916
	Declared war on Romania	August 28, 1916
Great Britain	Declared war on Germany	August 4, 1914
	Declared war on the Austro-Hungarian Empire	August 12, 1914
	Declared war on Turkey	November 5, 1914
	Declared war on Bulgaria	October 15, 1915
Greece	Declared war on the Austro-Hungarian Empire, Bulgaria, Germany, and Turkey	June 27, 1917
Guatemala	Declared war on Germany	April 23, 1918
Haiti	Declared war on Germany	July 12, 1918
Honduras	Declared war on Germany	July 19, 1918
Italy	Declared war on the Austro-Hungarian Empire	May 23, 1915
Declared war on Turkey	August 21, 1915
	Declared war on Bulgaria	October 19, 1915
	Declared war on Germany	August 28, 1916
Japan	Declared war on Germany	August 23, 1914
	Declared war on the Austro-Hungarian Empire	August 25, 1914
Liberia	Declared war on Germany	August 4, 1917
Montenegro	Declared war on the Austro-Hungarian Empire	August 5, 1914
	Declared war on Germany	August 8, 1914
	Declared war on Bulgaria	October 15, 1915
Nicaragua	Declared war on Germany and the Austro-Hungarian Empire	May 8, 1918
Panama	Declared war on Germany	April 7, 1917
	Declared war on the Austro-Hungarian Empire	December 10, 1917
Peru	Severed relations with Germany	October 6, 1917
Portugal	See Germany and the Austro-Hungarian Empire in this table
Romania	Declared war on The Austro-Hungarian Empire	August 27, 1916
	Capitulated to Central Powers by Treaty of Bucharest	May 7, 1918
	Re-entered the war on the side of the Allies	November 10, 1918
Russia	Declared war on Turkey	November 2, 1914
Declared war on Bulgaria	October 19, 1915
San Marino	Declared war on the Austro-Hungarian Empire	June 3, 1915
Serbia	Declared war on Germany	August 6, 1914
	Declared war on Turkey	November 2, 1914
Siam	Declared war on Germany and the Austro-Hungarian Empire	July 22, 1917
Turkey	Declared war on Romania	August 30, 1916
	Severed relations with the United States	April 23, 1917
United States	Declared war on Germany	April 6, 1917
	Declared war on the Austro-Hungarian Empire	December 7, 1917
Uruguay	Severed relations with Germany	October 7, 1917