(from the Funk & Wagnalls New Encyclopaedia, 1983, Volume 27, p 418)

Declarations of War

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