1The Horcrux hunt is stupid II
It all started with a nightmare. Harry dreamt of a stormy sea, waves battering an old wooden sailing ship as lightning and thunder smashed down around it. On board stood Voldemort, manically laughing and caressing a stone, whispering "my soul, my soul, fear not, you're safe, fear not this stormy sea. Have rest my soul, rest safe 'n sound, forever you are FFRREEEE!"
And then, looking straight at Harry, he chucked the rock overboard. Harry awoke screaming.
Harry was embarrassed to wake up Ron and Hermione, who needed all the rest they could get given their uncomfortable camping trip and the burden of carrying the Locket. But he couldn't fall asleep again, haunted as he was by the thought that their entire Horcrux hunt could be futile. What if what he'd seen was true? What if there rock-shaped Horcrux (for that it must've been) on the bottom of the North Sea? How could they hope to find it?
As the first rays of the sun rose over the horizon it dawned on him. He'd call it an epiphany. If their whole plan relied on Voldemort to hide his Horcruxes in findable predicable locations, they where going about it all wrong. Harry needed a new plan.
It was Hermione who came up with a better plan in the end. Well, she wanted to give Harry the credit. Not that the plan made Harry particularly proud. They'd just go to Ilvermorny and hope someone there could help.
It turned out magic made it rather easy to steal seats on a flight. Even if they drew attention from the muggles due to not knowing how airports work.
Oh, and Harry encased the Cursed Locket in rock, which made the thing a lot more manageable. If one rock had enough dignity for Voldemort's soul, his Harry-made rock did too.
The headmaster of Ilvermorny was kind and willing to help, though he didn't want to openly oppose Voldemort. The man had a bit of a reputation already. But the headmaster put them in touch with someone from MEDUSA, who passed their message on to a spook, who finally introduced them to a ritual expert and spell crafter that volunteered. A certain Mr Dearborn.
Mr Dearborn was even willing to host Harry and his friends whilst he studied the Horcrux. They eagerly accepted (after Hermione talked some sense into Harry) and trained and prepared themselves in relative comfort.
A month passed, and then another, and finally Mr Dearborn called the trio in to discuss his findings. "It doesn't make sense," he said and then repeated, "but I keep coming to the same answer."
"The pronunciation of the spell that lets you kill all of Voldemort by targeting this Horcrux, and the wand movement, are the same as those of the killing curse."
"You'll have to be very clear in your intent. The same spell can either destroy only the locket, or only the soul fragment in the locket, or all Voldemort's soul fragments, or all of them except the one in his body, or you can destroy all the vessels of his soul fragments including his body… You get the picture."
Harry nodded, and prepared himself. They discussed what would be best, and not wanting to destroy any of the founder's artefacts decided Harry would try to destroy all the soul pieces, and only the soul pieces.
So the next day Harry cast the spell. "Avada Kedavra." A green beam hit the locket, and it was instantly cleansed. At that very moment Voldemort dropped dead, the dark marks disappeared, and the blood purists won the second blood war.
"Wait, the blood purists won the war?" you say? Well of course they did. The Wizengamot makes the laws and acts as the court of appeals, and in the Wizengamot the blood purists were able to take their hereditary seats whilst half the progressives families were extinct or away. With the right laws and judges, people could return from Azkaban, but no-one returns from the dead. With the right bribes they could even obtain a super-majority, so that they could re-write the constitution. Which they did.
And with the law behind them (and Dumbledore dead) who could stand against?
Mercifully it would be a few years before Harry, Hermione and the others realised the shear depth of their defeat. They bounced back, eventually. But that is a story for another time.