There were several reasons The Great War started, one being the various alliances. These guaranteed that if two countries have a war than the whole world would get involved.
When the Archduke Franz Ferdinand was assassinated, it started the chain reaction that caused The Great War.
- Austria-Hungary declared war on Serbia.
- Russia was allied with Serbia, leading to a declaration of war on Austria-Hungary.
- Germany saw Russia mobilizing, and declared war on Russia, for Austria-Hungary.
- France was allied to Russia so they attacked Germany and Austria-Hungary.
- Germany then attacked France pulling Britain into the war.
- Then Japan entered the war because of there alliance to Britain.