On October 31, 1981 Age of Darkness canon begins. In this world, Harry Potter is the Boy-Who-Died.
On Halloween 1981, Peter Pettigrew visited James and Lily Potter. They had dinner, and Pettigrew shared news of the outside world where they were no longer allowed to venture. After dinner, Peter offered to put the young baby Harry to bed. But on the way to the nursery, he Apparated out of the house. He took the baby directly to Lord Voldemort. With no one to save him, Harry was killed. Back home, distraught and with no way of knowing what had happened to their son, the Potters contacted Albus Dumbledore.
Dumbledore used his connections to track down Voldemort, but by then it was too late. Faced with the reality of Harry’s limp body, Albus Dumbledore’s heart was broken. They duelled, and Voldemort emerged victorious again. Before long, the wizarding world was entirely under Lord Voldemort’s control. The Minister for Magic was deposed and all wizarding institutions including Hogwarts and St. Mungo’s Hospital for Magical Maladies and Injuries were temporarily shut down. After a year, all the high-ranking officials were in the charge of the Dementors and the all of wizarding society including the Order of the Phoenix were chased into hiding or forced to swear allegiance to Voldemort. By 1995, Voldemort had the United Kingdom entirely under his control and had started to turn his attention to the rest of the world.