Why is July and a half a Ghost Festival? What happened in history?

July 15 is a "ghost festival", probably because people burn paper money to worship their ancestors from the first half of July to 15. This atmosphere of dialogue between man and soul leads people to say "Ghost Festival".

In the China Folk Ghost Festival, the first day of July is the opening of the gate of hell, and the dead ancestors will return to the world to see if their descendants are good or evil, and future generations will also take the opportunity to sacrifice; July 15 is Ghost Festival. After July 15, the gate of hell is closed. Before July 30th, if someone has not offered sacrifices to his ancestors, his ancestors will wander around the world for a year. ?