Answer:
1) July 28, 1914
2) the assassination of Archduke Franz Ferdinand of Austria-Hungary.
3) Germany, Austria-Hungary, Bulgaria, the Ottoman Empire, Great Britain, France, Russia, Italy, Romania, Japan and the United States
Explanation:
The first world war started on July 28, 1914. The assassination of Archduke Franz Ferdinand of Austria-Hungary was the main cause of starting world war 1. When Russia defend its alliance Serbia, Germany declared war against Russia and the world war begin. During the war, Germany, Bulgaria, the Ottoman Empire and Austria-Hungary were on one side while France, Russia, Britain, Italy, Romania, Japan and the United States on the other side.
