LIST of BELLIGERENT STATES in the FIRST WORLD WAR - in Chronological Order

This is as complete a list as I can create from various sources. I cannot find any mention of the United States declaring war on Turkey or Bulgaria

If there are any missing declarations or any leads on the missing dates, I would be grateful for details.

The list doesn't include any of the new states created as a result of the Russian & Austrian defeats (Yugoslavia, Ukraine, Transcaucasus etc)

The lay-out of this page was originally designed by Nick Luft from data supplied by Jon Casey.

Country Declaring War Recipient Date Declaration Made
Austria-Hungary Serbia 28th July 1914
Germany Russia 1st August 1914
Germany France 3rd August 1914
Germany Belgium 4th August 1914
Britain Germany 4th August 1914
Austria-Hungary Russia 6th August 1914
Austria-Hungary Belgium ?? August 1914
Montenegro Austria-Hungary 7th August 1914
Germany Serbia* 9th August 1914
Montenegro Germany* 9th August 1914
France Austria-Hungary 10th August 1914
Britain Austria-Hungary 12th August 1914
Japan Germany 23rd August 1914
Japan Austria-Hungary 26th August 1914
Turkey Britain, France, Russia 5th November 1914#
Italy Austria-Hungary 23rd May 1915
Italy Turkey 20th August 1915
Bulgaria Serbia 12th October 1915
Britain Bulgaria 14th October 1915
France Bulgaria ?? October 1915
Russia Bulgaria ?? October 1915
Italy Bulgaria 20th October 1915
Albania Austria-Hungary* ?? January 1916
Germany Portugal 10th March 1916
Austria-Hungary Portugal* ?? March 1916
Rumania Austria-Hungary 27th August 1916
Germany Rumania 27th August 1916
Italy Germany 28th August 1916
Turkey Rumania 30th August 1916
Bulgaria Rumania 1st September 1916
USA Germany 6th April 1917
Cuba Germany 7th April 1917
Panama Germany 7th April 1917
Guatemala Germany 27th April 1917##
Nicaragua Germany 8th May 1917
Greece Central Powers 30th June 1917
Siam Central Powers 22nd July 1917
Liberia Germany 7th August 1917
China Germany 14th August 1917
Brazil Germany 26th October 1917
USA Austria-Hungary 7th December 1917
Panama Austria-Hungary 10th December 1917
Cuba Austria-Hungary 11th December 1917
Costa Rica Germany 23rd May 1918
Haiti Germany 12th July 1918
Honduras Germany 19th July 1918


Germany occupied Luxembourg on 1st August without a declaration of war.
* or possibly the other way round.
# Hostilities actually began on 31st October
## Actually a breaking of diplomatic relations which Guatemala subsequently decided to treat as a declaration of war.

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