system
Given the following post, respond as if you're commenting on Reddit:
human
[Lord of the Rings] If Sauron regained The One Ring, why would that ensure that evil would triumph eternally? How would he be any more of a threat than he was already? What is to stop someone just cutting the ring off of Sauron's finger again and starting the whole cycle over once more?

Even assuming that Sauron could regain his corporeal body and use the ring if it was returned to his possession, it's not like he was utterly unstoppable when he possessed the ring. He had been defeated in battle and forced to retreat in the battle of Gwathlo, and taken as a prison in Numenor, even before the Last Alliance of Men and Elves defeated him in the battle of Dagorlad. His new military was continuously losing to the forces of good while the Fellowship had been taking the ring to Mount Doom, so it's not like his new army would deliver any better results for him than his old one. He had lost the manufacturing power of Isengard, all of the Orcs Sauraman had been breeding were defeated, and any allies from Harad had long since fled. All of this happening didn't really depend on Sauron getting the ring or not  


You can say that Sauron would just know to expect that trick used on him again, but the siege of Barad-Dur kind of proves that he can be forced into joining the fray himself, and once he is forced into a fight, if the entire army knows his weak point and aims to damage his hand, of course he would lose the ring again.  


He also still retains absolute control over the Nazgul, so it's not like he ever stopped using the Ring of Power to control the wearers of the other rings. So if Sauron regained the ring, what would materially change about the heroes situation, and the War of the Ring in general?
gpt
Well, you've hit on one important thing already:

Sauron didn't need the Ring to win. The Ring had to be destroyed not because he would win if he found the Ring, but because destroying the Ring was the only way to stop him before he inevitably won.

>His new military was continuously losing to the forces of good while the Fellowship had been taking the ring to Mount Doom

Not really. He was not going all-out against them and the wins they were pulling off were costly and often reliant on one-time advantages or even outright miracles they wouldn't be able to rely on if he kept pressing the attack. You can ask about why it wouldn't go the same way it did during the Last Alliance, but there are no forces of Men or Elves on that scale anywhere in Middle-Earth anymore by the War of the Ring-- the good guys simply aren't that strong anymore.

However, having the Ring would have made it much easier for him to dominate and coordinate his forces, making the war a lot easier for him. Worse, it would give him direct control over the Three, which would mean one of two things happens. Either Gandalf, Elrond, and Galadriel have to ditch *their* rings fast, leaving Lothlorien and Rivendell defenseless and Gandalf with his own power to motivate and coordinate the free peoples significantly reduced, or he gains direct mental control over three of the most magically powerful leaders among the other side-- they serve him just as the Nazgul do. (And likely without anybody *knowing* he's just turned them into his personal Pokemon.)