This is a list of countries that participated in World War I, sorted by alphabetical order.
The Entente Forces
Note: The Entente Forces are sometimes also referred to as the Entente Powers or Allies of World War I.
- Vorlage:Flagicon Albania
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- Vorlage:Flagicon Czechoslovak Legions
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- Vorlage:Flagicon France
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- Vorlage:Flagicon Montenegro
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- Vorlage:Flagicon Portugal
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- Vorlage:Flagicon Siam (now Thailand)
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- Vorlage:Flagicon United States
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The Central Powers
- Vorlage:Flag (now Austria, Bosnia and Herzegovina, Croatia, Czech Republic, Hungary, parts of northeast Italy, partially Poland, partially Romania, Slovakia, Slovenia, partially Ukraine)
- Vorlage:Flagcountry (now Bulgaria, partially Greece, partially Republic of Macedonia)
- Vorlage:Flagcountry (now Burundi, Cameroon, small parts of People's Republic of China, partially Gabon, Germany, partially Ghana, Marshall Islands, Federated States of Micronesia, Namibia, northeastern Nigeria, Palau, northern Papua New Guinea, partially Poland, partially Republic of the Congo, Rwanda, Samoa, mainland Tanzania, and Togo)
- Vorlage:Flag (now Iraq, Israel, Jordan, Lebanon, partially Saudi Arabia, Syria, most of Turkey)
Neutral states
- Vorlage:Flagicon Afghanistan - Did not support or oppose any nation.
- Vorlage:Flag - Ally to US by treaty (see ABC countries for more information)
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- Vorlage:Flag - Ally to US by treaty (see ABC countries for more information)
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- Vorlage:Flag - Traded with both sides.
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- Vorlage:Flagicon Ethiopia
- Vorlage:Flag - Had a customs and monetary union with Austria-Hungary.
- Vorlage:Flagicon Luxembourg - Never declared war on the Central Powers despite being invaded and occupied by Germany.
- Vorlage:Flagicon Vorlage:Flag - Declined an alliance with Germany (see Zimmermann Telegram). An ally to the United States by treaty (see ABC countries).
- Vorlage:Flagicon Netherlands - An ally of the United Kingdom by treaty. Traded with both sides.
- Vorlage:Flag - Gave naval assistance to the United Kingdom.
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- Vorlage:Flagicon image Persia - Occupied by British and Russian troops.
- Vorlage:Flagicon Spain - Also treaty bound ally to the United Kingdom.
- Vorlage:Flag - Financially supported Germany.
- Vorlage:Flag - Switzerland did declare a "state of siege".
- Vorlage:Flag - Supplied the Allies with oil.
Declarations of War
The following table shows the timeline of the several declarations of war Vorlage:Ref among the belligerent powers.
Notes
- Vorlage:Note The British Empire was the common term for the United Kingdom and its overseas possessions at this time. The term refers to the colonies it controlled, to the Indian Empire, which, while not officially designated a colony, was functionally indistinguishable from one, and the British Dominions - former colonies which were self-governing in most respects but whose foreign policy was controlled by London; Australia, Canada, Newfoundland, New Zealand and South Africa. At that time, the United Kingdom of Great Britain and Ireland also included the entire island of Ireland.
- Vorlage:Note Entries on a yellowish background refer to severed diplomatic relations only, not to actual declarations of war
