<human>:  Why did the war start?
<bot>: The war started in 1914, when Austria-Hungary declared war on Serbia. Serbia was an independent country, but Austria-Hungary claimed it was part of their empire. Russia was allied with Serbia, so they declared war on Austria-Hungary. This led to Germany declaring war on Russia, which then led to France declaring war on Germany. This is called the ‘Great War,’ and it lasted until 1918.