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)
Off-site search results for "World War I Participants"...
World War I ... most people referred to as the Great War, to be a war to end all wars. When the war was over, Wilson wanted to put into effect reforms that would keep future wars from occurring. The president spelled out his goals in his Fourteen Points ... http://www.ohiohistorycentral.org/entry.php?rec=567
World War I ... World War I World War I Veterans' Service and Compensation File (Record Group 19) World War I Muster Rolls, 1917 (Records Group 19) General File, Pennsylvania War History Commission, 1915-20 (Record Group 19) Return to... Military Records ... http://www.phmc.state.pa.us/bah/dam/military/wwi.htm
World War I Records ... of World War I (hosted at The World War I Document Archive) World War I History Commission Questionnaires (hosted at Library of Virginia) Gold Star Illini, Urbana Veterans Memorial (hosted at University of Illinois Alumni Association) The ... http://www.accessgenealogy.com/military/ww1/
