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human
[Harry Potter] What if Voldemort had targeted Neville Longbottom and his family instead?

The perfect overheard by Snape could have meant Harry or Neville, if Voldemort had instead decided it wasn't Harry that the prophecy had described but instead that it was Neville.

To start, Severus Snape does not betray Voldemort as Lilly Potter is not the target, Voldemort murders Frank and Alice Longbottom. Does Neville survive? If so, Bellatrix Lestrange, Barty Crouch Jr, Rodolphus and Rabastan Lestrange attempt to retaliate by targeting Lilly and James Potter to find the whereabouts of Voldemort. Is Snape aware of this and can he warn them of the plan? Do the Potters get tortured into insanity? If they do Harry goes to Sirius as he is not a criminal.

How do the lives of both these characters change and how do the events of the 7 books change?
gpt
Neville doesn't survive, and even if he did, Bellatrix, BC Jr. and crew wouldn't go after the Potters. There were a very specific set of circumstances that set off the protection magic that stopped Voldemort the first time. Voldemort's attack on the Longbottom's would play out differently enough that Neville wouldn't receive that protection. The protection magic that saves Harry is triggered by a sacrifice. 

Basically, Neville's parents were Aurors, and apparently good enough at their jobs to earn the respect of people like Barty Crouch Sr. and Mad-Eye Moody. Harry's parents were kids. When Voldemort attacked, James Potter had left his wand in another room. Lily ran upstairs with Harry. Both of them put themselves between Voldemort and Harry, and neither of them resisted Voldemort magically. Neville's parents would not have been unprepared, and would have fought Voldemort. They would have died fighting, and thus Neville would not receive the same protection Harry did. 

But the prophecy ISN'T about Neville. This is kind of a key point. The part that Snape overhears could apply to Harry or Neville, but he's discovered before he hears the final part: Voldemort will mark his equal. Harry is half-blood, just like Voldemort. By Voldemort's appraisal, this makes them equals. The prophecy isn't fulfilled by Voldemort killing the Potters, that's where it begins.