What Caused the First World War?

Austria used the assassination to attack Serbia. In order to do this, they asked for the support of Germany. Although the German leaders were aware of the domino effect of attacking Serbia, they supported Austria.
Since Germany and Austria wanted a quick attack on Serbia, so that other countries would not get involved, an ultimatum was sent. When the ultimatum was sent to Serbia in July 23,1914, which demanded Serbia to abolish all 'anti-Austrian activities', and allow Austria to investigate the assassination of Francis Ferdinand. Serbia accepted to the ultimatum, but did not allow Austria to investigate the murder. This caused Austria to declare war on Serbia on July 28.
When Austria attacked Serbia, as the German leaders had anticipated, Russia prepared to attack Austria. Germany warned Russia to stop the preparation, but because Russia did not listen, Germany attacked Russia on August 1. Two days later, Germany also declared war against France which was Russia's ally.
Germany planned to invade France through Belgium, but unfortunately Belgium refused this. On August 3, Germany invaded Belgium. …