50 years building homestead & sculptor utopia amid redwoods

What If Grindelwald WON and RULED the Wizarding World - Harry Potter Theory

The proper inflection point would have been Dumbledore accepting the nomination of the Chillin and becoming Mugwump. In that case, there would have been no duel. Muggle history would have also changed, as it could be argued that Grindelwald would have been in league with Hitler. Albus would never have allowed Hitler to retain power - he would have intervened in Muggle affairs rather than keeping the magical community out of the war.

At some point, secrecy would have been abandoned. Grindelwald may have taken up with Stalin, rather than Hitler, and the Cold War would have happened anyway, but without the Bomb - which Albus would have never allowed to have been developed. Albus would not have been at Hogwarts, so someone else would have been dealing with Riddle - who Slughorn would have given the job as Defense Against the Dark Arts teacher. He may not have been self-radicalized and there would have been no prophesy nor duel nor death eaters. Riddle may have simply become Headmaster in time, Minister of Magic or Mugwump for NATO. He would have dueled Grindelwald for the Elder Wand.

James Potter may have been Slytherin and an acolyte of Riddle, with Snape a Gryffindor in the alternate universe and would have ended up with Lilly and would not have been a death eater (there would not have been such things). Without being traumatized by the Marauders, his son would have been a potions master and would have ended up with Hermione because they would have been good students together.

James would have married one of the the Black sisters and would have been the father of Narcissa's son or Bellatrix's daughter - and maybe more than one. That child would have been a twin, brother or cousin of Draco - both of whom would have had glasses and been the Potter twins - rivals or co-conspirators to the Weasley twins. Without the death eater movement, Crabbe and Goyle would have been in Hufflepuff and leaders of the Hogwarts Pride Movement. 

If the Weasley Twins and Potter Twins were friendly rivals, Ginny would have ended up with one of them. Both sets of twins would have probably been members of the RAF or whatever NATO force Albus or Riddle was in charge of. Riddle would have married Minerva, who would have further tempered his behavior and they would have lived in Number 10 - although Minerva might have been like Thatcher instead.

Grindelwald would have been an excellent acolyte of Stalin, but with time would have tempered his slave the Muggles ideology. He would have been a good Party Member and probably would have taken over for Stalin and never been deposed. His eventual disciple would be where Putin is now. There never would have been Gorbachev (or Reagan), although Russia would not have been as backward under magical rule. Authoritarians love to be loved. He would have bought off the Muggles in either scenario because it is cheaper to have happy peasants than enslaved ones.