World War One officially began on July 28, 1914..
28 July 1914 Austria-Hungary declared war on Serbia
World War One officially ended on November 11, 1918
All Declarations of War by Date Order:
- 28 July 1914 Austria-Hungary declared war on Serbia
- 1 August 1914 Germany declared war on Russia
- 3 August 1914 Germany declared war on France
- 4 August 1914 Germany declared war on Belgium
- 4 August 1914 United Kingdom declared war on Germany
- 5 August 1914 Montenegro declared war on Austria-Hungary
- 6 August 1914 Austria-Hungary declared war on Russia
- 6 August 1914 Serbia declared war on Germany
- 9 August 1914 Montenegro declared war on Germany
- 11 August 1914 France declared war on Austria-Hungary
- 12 August 1914 United Kingdom declared war on Austria-Hungary
- 22 August 1914 Austria-Hungary declared war on Belgium
- 23 August 1914 Japan declared war on Germany
- 25 August 1914 Japan declared war on Austria-Hungary
- 1 November 1914 Russia declared war on Ottoman Empire
- 2 November 1914 Serbia declared war on Ottoman Empire
- 3 November 1914 Montenegro declared war on Ottoman Empire
- 5 November 1914 United Kingdom declared war on Ottoman Empire
- 5 November 1914 France declared war on Ottoman Empire
- 23 May 1915 Italy declared war on Austria-Hungary
- 3 June 1915 San Marino declared war on Austria-Hungary
- 21 August 1915 Italy declared war on Ottoman Empire
- 14 October 1915 Bulgaria declared war on Serbia
- 15 October 1915 United Kingdom declared war on Bulgaria
- 15 October 1915 Montenegro declared war on Bulgaria
- 16 October 1915 France declared war on Bulgaria
- 19 October 1915 Italy declared war on Bulgaria
- 19 October 1915 Russia declared war on Bulgaria
- 9 March 1916 Germany declared war on Portugal
- 15 March 1916 Austria-Hungary declared war on Portugal
- 27 August 1916 Romania declared war on Austria-Hungary
- 27 August 1916 Italy declared war on Germany
- 28 August 1916 Germany declared war on Romania
- 30 August 1916 Ottoman Empire declared war on Romania
- 1 November 1916 Bulgaria declared war on Romania
- 6 April 1917 United States declared war on Germany
- 7 April 1917 Cuba declared war on Germany
- 10 April 1917 Bulgaria declared war on United States
- 13 April 1917 Bolivia declared war on Germany
- 20 April 1917 Ottoman Empire declared war on United States
- 2 July 1917 Greece declared war on Germany
- 2 July 1917 Greece declared war on Austria-Hungary
- 2 July 1917 Greece declared war on Ottoman Empire
- 2 July 1917 Greece declared war on Bulgaria
- 22 July 1917 Siam declared war on Germany
- 22 July 1917 Siam declared war on Austria-Hungary
- 4 August 1917 Liberia declared war on Germany
- 14 August 1917 China declared war on Germany
- 14 August 1917 China declared war on Austria-Hungary
- 6 October 1917 Peru declared war on Germany
- 7 October 1917 Uruguay declared war on Germany
- 26 October 1917 Brazil declared war on Germany
- 7 December 1917 United States declared war on Austria-Hungary
- 7 December 1917 Ecuador declared war on Germany
- 10 December 1917 Panama declared war on Austria-Hungary
- 16 December 1917 Cuba declared war on Austria-Hungary
- 23 April 1918 Guatemala declared war on Germany
- 8 May 1918 Nicaragua declared war on Germany
- 8 May 1918 Nicaragua declared war on Austria-Hungary
- 23 May 1918 Costa Rica declared war on Germany
- 12 July 1918 Haiti declared war on Germany
- 19 July 1918 Honduras declared war on Germany
- 10 November 1918 Romania declared war on Germany
The Central Powers declarations of war during World War One were:
In Date Order
German Declarations of War
- 1 August 1914 Germany declared war on Russia
- 3 August 1914 Germany declared war on France
- 4 August 1914 Germany declared war on Belgium
- 9 March 1916 Germany declared war on Portugal
- 28 August 1916 Germany declared war on Romania
Austria-Hungary Declarations of War
- 28 July 1914 Austria-Hungary declared war on Serbia
- 6 August 1914 Austria-Hungary declared war on Russia
- 22 August 1914 Austria-Hungary declared war on Belgium
- 15 March 1916 Austria-Hungary declared war on Portugal
Bulgarian Declarations of War
- 14 October 1915 Bulgaria declared war on Serbia
- 1 November 1916 Bulgaria declared war on Romania
- 10 April 1917 Bulgaria declared war on United States
Ottoman Empire Declarations of War
- 30 August 1916 Ottoman Empire declared war on Romania
- 20 April 1917 Ottoman Empire declared war on United States
The Allied Forces declarations of war during World War One were:
- 4 August 1914 United Kingdom declared war on Germany
- 5 August 1914 Montenegro declared war on Austria-Hungary
- 6 August 1914 Serbia declared war on Germany
- 9 August 1914 Montenegro declared war on Germany
- 11 August 1914 France declared war on Austria-Hungary
- 12 August 1914 United Kingdom declared war on Austria-Hungary
- 23 August 1914 Japan declared war on Germany
- 25 August 1914 Japan declared war on Austria-Hungary
- 1 November 1914 Russia declared war on Ottoman Empire
- 2 November 1914 Serbia declared war on Ottoman Empire
- 3 November 1914 Montenegro declared war on Ottoman Empire
- 5 November 1914 United Kingdom declared war on Ottoman Empire
- 5 November 1914 France declared war on Ottoman Empire
- 23 May 1915 Italy declared war on Austria-Hungary
- 3 June 1915 San Marino declared war on Austria-Hungary
- 21 August 1915 Italy declared war on Ottoman Empire
- 15 October 1915 United Kingdom declared war on Bulgaria
- 15 October 1915 Montenegro declared war on Bulgaria
- 16 October 1915 France declared war on Bulgaria
- 19 October 1915 Italy declared war on Bulgaria
- 19 October 1915 Russia declared war on Bulgaria
- 27 August 1916 Romania declared war on Austria-Hungary
- 27 August 1916 Italy declared war on Germany
- 6 April 1917 United States declared war on Germany
- 7 April 1917 Cuba declared war on Germany
- 13 April 1917 Bolivia declared war on Germany
- 2 July 1917 Greece declared war on Germany
- 2 July 1917 Greece declared war on Austria-Hungary
- 2 July 1917 Greece declared war on Ottoman Empire
- 2 July 1917 Greece declared war on Bulgaria
- 22 July 1917 Siam declared war on Germany
- 22 July 1917 Siam declared war on Austria-Hungary
- 4 August 1917 Liberia declared war on Germany
- 14 August 1917 China declared war on Germany
- 14 August 1917 China declared war on Austria-Hungary
- 6 October 1917 Peru declared war on Germany
- 7 October 1917 Uruguay declared war on Germany
- 26 October 1917 Brazil declared war on Germany
- 7 December 1917 United States declared war on Austria-Hungary
- 7 December 1917 Ecuador declared war on Germany
- 10 December 1917 Panama declared war on Austria-Hungary
- 16 December 1917 Cuba declared war on Austria-Hungary
- 23 April 1918 Guatemala declared war on Germany
- 8 May 1918 Nicaragua declared war on Germany
- 8 May 1918 Nicaragua declared war on Austria-Hungary
- 23 May 1918 Costa Rica declared war on Germany
- 12 July 1918 Haiti declared war on Germany
- 19 July 1918 Honduras declared war on Germany
- 10 November 1918 Romania declared war on Germany
Declarations of War By Country Order:
Against Germany
- 4 August 1914 United Kingdom declared war on Germany
- 6 August 1914 Serbia declared war on Germany
- 9 August 1914 Montenegro declared war on Germany
- 23 August 1914 Japan declared war on Germany
- 27 August 1916 Italy declared war on Germany
- 6 April 1917 United States declared war on Germany
- 7 April 1917 Cuba declared war on Germany
- 13 April 1917 Bolivia declared war on Germany
- 2 July 1917 Greece declared war on Germany
- 22 July 1917 Siam declared war on Germany
- 4 August 1917 Liberia declared war on Germany
- 14 August 1917 China declared war on Germany
- 6 October 1917 Peru declared war on Germany
- 7 October 1917 Uruguay declared war on Germany
- 26 October 1917 Brazil declared war on Germany
- 7 December 1917 Ecuador declared war on Germany
- 23 April 1918 Guatemala declared war on Germany
- 8 May 1918 Nicaragua declared war on Germany
- 23 May 1918 Costa Rica declared war on Germany
- 12 July 1918 Haiti declared war on Germany
- 19 July 1918 Honduras declared war on Germany
- 10 November 1918 Romania declared war on Germany
Against Austria-Hungary
- 5 August 1914 Montenegro declared war on Austria-Hungary
- 11 August 1914 France declared war on Austria-Hungary
- 12 August 1914 United Kingdom declared war on Austria-Hungary
- 25 August 1914 Japan declared war on Austria-Hungary
- 23 May 1915 Italy declared war on Austria-Hungary
- 3 June 1915 San Marino declared war on Austria-Hungary
- 27 August 1916 Romania declared war on Austria-Hungary
- 2 July 1917 Greece declared war on Austria-Hungary
- 22 July 1917 Siam declared war on Austria-Hungary
- 14 August 1917 China declared war on Austria-Hungary
- 7 December 1917 United States declared war on Austria-Hungary
- 10 December 1917 Panama declared war on Austria-Hungary
- 16 December 1917 Cuba declared war on Austria-Hungary
- 8 May 1918 Nicaragua declared war on Austria-Hungary
Against Ottoman Empire
- 1 November 1914 Russia declared war on Ottoman Empire
- 2 November 1914 Serbia declared war on Ottoman Empire
- 3 November 1914 Montenegro declared war on Ottoman Empire
- 5 November 1914 United Kingdom declared war on Ottoman Empire
- 5 November 1914 France declared war on Ottoman Empire
- 21 August 1915 Italy declared war on Ottoman Empire
- 2 July 1917 Greece declared war on Ottoman Empire
Against Bulgaria
- 15 October 1915 United Kingdom declared war on Bulgaria
- 15 October 1915 Montenegro declared war on Bulgaria
- 16 October 1915 France declared war on Bulgaria
- 19 October 1915 Italy declared war on Bulgaria
- 19 October 1915 Russia declared war on Bulgaria
- 2 July 1917 Greece declared war on Bulgaria
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