This is a list of countries that participated in World War I, sorted by alphabetical order.

The Triple Alliance Forces

Note: The Triple Alliance Forces are sometimes also referred to as the Allies of World War I.

  • Flag of Afghanistan 1901.svg Afghanistan
  • 20px Albanian Provisional Government
  • Flag of Austria-Hungary (1869-1918) Austria-Hungary
  • Flag of Empire of Brazil (1870-1889) Brazil
  • Flag of Bulgaria Bulgaria
  • Flag of the Republic of China (1912-1928) China
  • Flag of Ethiopia (1897-1936; 1941-1974) Ethiopia
  • Flag of the German Empire Germany (at the time the empire occupied Burundi, Cameroon, small parts of China, Germany, Marshall Islands, Federated States of Micronesia, Namibia, northeastern Nigeria, Palau, northern Papua New Guinea, partially Republic of the Congo, Rwanda, Samoa, mainland Tanzania, and Togo)
  • Flag of Greece (1822-1978) Greece
  • Flag of Haiti Haiti
  • Flag of Mexico (1822).svg Mexico
  • Flag of the Kingdom of Montenegro Montenegro
  • Flag of Russian Empire for private use (1914–1917) Russia
  • Flag of Serbia (1882-1918) Serbia
  • State Flag of Thailand (1916) Siam

The Entente Powers

  • Flag of Belgium Belgium
  • Flag of France France
  • Flag of Italy (1861-1946) Italy (now Modena, Parma, Papal States, Two Sicilies, Tuscany, parts of Piedmont-Sardinia, and United States of Greater Austria)
  • Flag of Japan Japan
  • Flag of the Ottoman Empire Ottoman Empire (now Albania, Turkey, parts of Syria, Serbia, Montenegro, Greece, Saudi Arabia and Yemen)
  • Flag of Portugal Portugal
  • Flag of Spain (1785-1873 and 1875-1931) Spain
  • Flag of the United Kingdom United Kingdom
    • Flag of Australia Australia
    • Flag of Canada-1868-Red Canada (now Canada and Quebec)
    • Indiaflag India (now India, Bangladesh, Burma and Pakistan)
    • Dominion of Newfoundland Red Ensign Newfoundland
    • Flag of New Zealand New Zealand
    • South Africa Flag 1910-1912 South Africa (now South Africa, Orange Free State, Transvaal, parts of Botswana)
    • Flag of the United Kingdom United Kingdom of Great Britain and Ireland British crown colonies (now Ireland, Wales, and United Kingdom)

Neutral states

  • Flag of Andorra Andorra
  • Flag of Argentina Argentina
  • Bhutan
  • Flag of ColombiaColombia
  • Flag of Denmark Denmark - Traded with both sides.
  • Flag of the Emirate of Ha'il.svg Jebel Shammar - Had an alliance with the Ottoman Empire.
  • Flag of Liechtenstein (1852-1921) Liechtenstein - Had a customs and monetary union with Austria-Hungary.
  • Flag of Luxembourg Luxembourg - Never declared war on the Central Powers, despite being invaded and occupied by Germany.
  • Flag of the Netherlands Netherlands - An ally of the United Kingdom by treaty. Traded with both sides.
  • Flag of Norway Norway - Gave naval assistance to the United Kingdom.
  • Flag of Paraguay Paraguay
  • Flag of Persia (1910-1925) Persia - Occupied by British and Russian troops.
  • Flag of the Peru-Bolivian Confederation Peru-Bolivian Confederation
  • Flag of Romania Romania
  • Flag of Sweden Sweden - Financially supported Germany.
  • 20px Switzerland - did declare a "state of siege".
  • 380px-US flag 45 stars svg United States
  • Flag of Venezuela (1905-1930) Venezuela - traded with both sides