world war 1 occurred in 1914.It started because of the assassination of Archduke Francis Ferdinand. The countries that were involved in world war 1 were
Allied states
Belgium (including Belgian colonial forces)
British Empire
Australia
British crown colonies
Canada
India
New Zealand
Newfoundland
South Africa
United Kingdom of Great Britain & Ireland
France (including French colonial forces)
Kingdom of Greece (May 1917 and after)
Kingdom of Italy (April 1915 and after)
Empire of Japan
Kingdom of Montenegro
Portugal (March 1916 and after) (including Portuguese colonial forces)
Kingdom of Romania (August 1916-May 1918)
Russian Empire (until November 1917)
Kingdom of Serbia
United States of America (April 1917 and after)
as well as:
Albania
Andorra
Armenia (May 1918 and after)
Bolivia (April 1917 and after)
Brazil (October 1917 and after)
China (August 1917 and after)
Costa Rica (May 1918 and after)
Cuba (April 1917 and after)
Czechoslovakia
Ecuador (December 1917 and after)
Guatemala (April 1918 and after)
Liberia (August 1917 and after)
Haiti (July 1918 and after)
Honduras (July 1918 and after)
Nicaragua (May 1918 and after)
Panama (December 1917 and after)
Peru (October 1917 and after)
San Marino (June 1915 and after)
Siam (July 1917 and after)
Uruguay (October 1917 and after)