This is a list of countries that participated in World War I, sorted by alphabetical order.
Note: The "Entente Powers" are also known as the Allies of World War I or the Allies
Andorra (declared war on Germany but sent only 10 troops to the fighting)
Armenia
Arab Rebels
Belgium (Belgian colonial empire)
Brazil
China
Costa Rica
Cuba
Czechoslovak Legions
Emirate of Nejd and Hasa
France (French colonial empire)
Greece
Guatemala
Haiti
Honduras
Italy (Italian Empire)
Japan
Liberia
Montenegro
Nepal
New Hebrides (British-French condominium)
Nicaragua
Panama
Portugal (Portuguese colonial empire)
Romania
Russia
Russian Republic
Russian SFSR until Treaty of Brest-Litovsk
Serbia
Siam (now Thailand)
United Kingdom (British Empire[1])
Canada
India (now India, Bangladesh, Burma and Pakistan)
Newfoundland
Australia
New Zealand
Malta
South Africa
Rhodesia (now Zimbabwe and Zambia), administered by the British South Africa Company
British crown colonies
United States
Alaska
Hawaii
Philippine Islands
Puerto Rico
Other unincorporated territories
Non Independent ethnic groups: Armenians, Assyrians, Poles, Pontic Greeks
Austria-Hungary
Azerbaijan Democratic Republic
Bulgaria
Banat Republic
Duchy of Courland and Semigallia (satellite state)
Dervish State
Democratic Republic of Georgia
Germany
German colonial empire
Jabal Shammar
Kingdom of Lithuania (satellite state)
Ottoman Empire
South African Republic
Senussi
Kingdom of Poland (satellite state)
Sultanate of Darfur
Ukrainian State
Afghanistan – received a German diplomatic mission trying to convince it to act against the British in India
Principality of Albania – In political chaos since the beginning of the war, the country was occupied by both Central and Allied powers but never declared war on either side
Argentina
Bolivia
Bhutan
Chile
Colombia
Denmark
Ecuador
El Salvador
Ethiopia – Supported Central Powers and was on the verge of entering the war before Iyasu V's dethronement
Iran – Civil dispute and Allied Campaign against Ottomans
Liechtenstein – Had a customs and monetary union with Austria-Hungary
Luxembourg – Never declared war on the Central Powers despite being invaded and occupied by Germany
Bogd Khaanate of Mongolia
/ Mexico – Declined an alliance with Germany (see Zimmermann Telegram)
Monaco
The Netherlands (Dutch Empire) – An ally of the United Kingdom by treaty. Traded with both sides.
Norway – Gave naval assistance to the United Kingdom.
Paraguay
Peru
San Marino - 20 volunteers joined on the Italian (Allied) side and it is claimed that San Marino was at war with Austria–Hungary, but it never entered the war
Spain (Spanish Territories in Africa)
Spitsbergen – Danish-Norwegian co-dominium
Sweden – Non-belligerent
Switzerland – Switzerland did declare a "state of siege"
Uruguay
Venezuela – Supplied the Allies with oil
The following table shows the timeline of the several declarations of war among the belligerent powers. Entries on a yellow background show severed diplomatic relations only, not actual declarations of war.
