Backstory

The war ended with the death of Voldemort and the capture of most of the death eaters. There were lot's of deaths for both sides.

When the war ended Dumbledore came out of hiding. Apparently he faked his death so he could go into hiding.

Dumledore thought that the muggle world should know about the wizard world. A lot of people agreed but there were some that disagreed. Harry and Hermione were a part of the disagreeing group. They knew that the muggles would not like the wizards and that it's human nature to destroy anything that is unknown or that they fear, basically a threat.

When the muggles found out most of the government started making equipment that would kill a wizard, because of an accident with a wizard and a muggle, muggles started hunting wizards down. In the accident a muggle got hurt because of the wizard so wizard were deemed dangerous. The wizards in Azkaban were the only ones safe as muggles had no way of fighting demeanors. There was also a few squibs being killed but not often.