Declarations of War 1914 July 28 Austria-Hungary on Serbia August 1 Germany on Russia August 2 German invasion of Luxembourg1 August 3 Germany on France August 4 German invasion of Belgium* August 4 Great Britain enters the war* August 6 Serbia on Germany August 6 Austria-Hungary on Russia August 7 Montenegro on Austria-Hungary August 11 France on Austria-Hungary August 12 Great Britain on Austria-Hungary August 12 Montenegro on Germany August 23 Japan on Germany August 23 Austria-Hungary on Japan August 28 Austria-Hungary on Belgium October 15 Montenegro on Bulgaria October 29 the …