Explanation:

The Austria-Hungary government saw the assassination as a direct attack on the country. They believed that the Serbians had helped the Bosnian terrorists in the attack. They made harsh demands on the Serbians which the Serbians rejected. At the same time, Russia began to mobilize their army to help protect Serbia. When Serbia rejected the demands, Austria-Hungary declared war on Serbia. A few days later, Germany declared war on Russia to help its ally Austria-Hungary. Then France began to mobilize to help its ally Russia, and Germany followed by declaring war on France. World War I had begun.