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World War I broke out with Austria-Hungary’s declaration of war against Serbia in July 1914. Soon, most of the major nations of the world were involved in armed conflict. Countries such as Australia, Canada, India, and New Zealand joined in as part of the British Empire. Other colonies of European nations were also embroiled in conflict, thus bringing in most countries of Asia and Africa to the war.
YEAR | DATE | DECLARATION OF WAR |
1914 | 28-Jul | Austria-Hungary declares war on Serbia. |
1-Aug | Germany declares war on Russia | |
3-Aug | Germany declares war on France | |
3-Aug | Germany invades Belgium | |
4-Aug | Britain declares war on Germany | |
5-Aug | Montenegro declares war on Austria-Hungary | |
6-Aug | Austria-Hungary declares war on Russia | |
6-Aug | Serbia declares war on Germany | |
8-Aug | Montenegro declares war on Germany | |
12-Aug | France declares war on Austria-Hungary | |
12-Aug | Britain declares war on Austria-Hungary | |
23-Aug | Japan declares war on Germany | |
25-Aug | Japan declares war on Austria-Hungary | |
28-Aug | Austria-Hungary declares war on Belgium | |
2-Nov | Russia declares war on the Ottoman Empire | |
2-Nov | Serbia declares war on the Ottoman Empire | |
3-Nov | Montenegro declares war on the Ottoman Empire | |
5-Nov | France declares war on the Ottoman Empire | |
5-Nov | Britain declares war on the Ottoman Empire | |
1915 | 23-May | Italy declares war on Austria-Hungary |
21-Aug | Italy declares war on the Ottoman Empire | |
14-Oct | Bulgaria declares war on Serbia | |
15-Oct | Montenegro declares war on Bulgaria | |
15-Oct | Britain declares war on Bulgaria | |
16-Oct | France declares war on Bulgaria | |
19-Oct | Italy declares war on Bulgaria | |
19-Oct | Russia declares war on Bulgaria | |
1916 | 9-Mar | Germany declares war on Portugal |
15-Mar | Austria-Hungary declares war on Portugal | |
27-Aug | Italy declares war on Germany | |
27-Aug | Romania declares war on Austria-Hungary | |
30-Aug | Ottoman Empire declares war on Romania | |
1-Sep | Bulgaria declares war on Romania | |
1917 | 6-Apr | USA declares war on Germany |
7-Apr | Panama declares war on Germany | |
27-Jun | Greece declares war with Austria-Hungary | |
27-Jun | Greece declares war with Germany | |
27-Jun | Greece declares war with Bulgaria | |
27-Jun | Greece declares war with the Ottoman Empire | |
7-Dec | USA declares war on Austria-Hungary | |
10-Dec | Panama declares war on Austria-Hungary | |
1918 | 23-Apr | Guatemala declares war on Germany |
8-May | Nicaragua declares war on Austria-Hungary | |
8-May | Nicaragua declares war on Germany | |
12-Jul | Haiti declares war on Germany | |
19-Jul | Honduras declares war on Germany |