What were the dates and major actors of the First World War and what was the main 'spark' that led to its outbreak?

Dates: 28th July 1914 - 11th November 1918

Major actors: Germany, Austria-Hungary, Italy, Serbia, France, Britain, Russia and the United States.

Main 'spark': Sarajevo assassinations of the heir, Archduke Franz Ferdinand, and his wife, to the Austria-Hungarian throne.