The Rocket's Red Glare

Why wasn't there international assistance against Voldemort? How can the American President be obliviated willy-nilly? Why was the 'dark school' Durmstrang allowed into the Triwizard Tournament, and do Brazilian students learn how to curse hats? Harry Potter's about to get a history lesson and a wake-up call. — Canon, takes place between the final battle and epilogue.