Wizards have revealed their magic to muggles. As you could expect, many purebloods did not agree with this. Tom Riddle decided to split those who believed in mixing with muggles and those who disagreed in mixing with muggles. Tom became the general of the purebloods, Albus Dumbledore became general of the muggles and wizards. Harry Potter is a mere speck of dust in the grand scheme of things. Can he change the future that is surely filled with misery and pain? I know I'm shit at summaries, sorry.