Countries involved in ww I (by time entering), Austria-Hungary 28 July 1914 1/1-389/3 Serbia 28 July 1914 1/1 Germany 1 Aug 1914 2/1 Russia 1 Aug 1914 2/1-328/3 France 3 Aug 1914 2/3 United Kingdom 4 Aug 1914 2/4 Japan 23 Aug 1914 7/3 Ottoman Empire 31 Oct 1914 20/4-388/3 Italy 23 May 1915 75/4-389/3 Bulgaria 20ct 1915 110/2-381/2 Portugal 9 March 1916 146/4 Romania 27 Aug 1916 190/2 United States 6 Apr 1917 246/4 Greece 26 June 1917 267/4 ww 1 End 11 Nov 1918 End Bar 392