What event caused the start of World War 1?

Answer 1

Firstly,

Bosnia-Herzegovinia were a country as part of the Austria-Hungrary empire. However many of their people wanted to be a part of Serbia's empire. Thus a protest group called the Black Hand Gang shot the heir to the Austria-Hungrary throne (Arch-Duke Franz Ferdinand).

This then led to Serbia looking to Russia for support and thus their ally France and Austria-Hungrary seeking the support of Germany. This then meant that Germany declared war on Russia and then France.

To get to France, Germany initiated the Schlieffen Plan which involved marching through Belgium, of whom Britain had promised to protect. When Germany went into Belgium, Britain ordered them to leave, when they didn't Britain were given an excuse to go to war with Germany of whom they feared their expansion accross Europe.

Hope this helps.