My guess - International Association of Quidditch, organized by Chairman Hassan Mostafa on the basis that Voldemort's free-flying threatens to undermine the integrity of the sport.

It doesn't matter who organizes it, a militarized magical Britain would prompt international wizard cooperation so that the members would keep their freedoms and the Statute would be maintained.

I agree with Damask that Voldemort at the end is too interested in personal power- he's the sort that always seeks a greater challenge match, so long as he wins in the end.

During his first rise he was focused on dominating their society accompanied by his loyal allies. When he returned they took up the plan that was already in motion, just going back a few steps to rearrange who they had to dominate in order to win, but he'd lost his mind and his reason for doing it, obsessing instead on trying to recapture his glory without remembering the underlying purpose.

I say this because he'd broken and humiliated his best power broker (Lucius), and taken to lashing out at his minions when they made mistakes (Avery, Rookwood). The first time through, they were helping him because he promised and delivered in granting them power and wealth. Upon his return his loyal subjects followed because they feared for their lives or they simply enjoyed having an excuse to be sadistic.

If we assume that Voldemort's mind would have stabilized once Harry was gone (and the ersatz Horcrux no longer throwing off his seven-part-soul groove), I could see him restructuring his plans.

1. End the 'dark period' of quelling rebellion, so that citizen wizards would be glad to accept a stricter rule than before but one much more lenient than the martial law phase.
2. Reorganize and retrain exceptional wizards to work as infiltrators, strike teams and public task forces.
3. Take over other magical nations, as subtly as possible but with overt force to back up the play.
4. Once his people ran the bulk of the Ministries, change policy to subjugate the muggles under wizard rule.
5. Bring about a new age of Pharoahs, all devoted to the serpent god Voldemort.
6. [by now we should have something new to try- music perhaps, or interstellar exploration, cooking, abomination-breeding, whatever]

 

That idea alone deserves a story.

 

I don't see how thats relevant to VOldemort winning every single fight against him, and thus preventing him from even being slightly killed. Even if he's a terrible war leader and political leader and economic leader, someone still needs to be good enough to fight him or they won't stand a chance.