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human
[Lord of the Rings] What would have happened if Isengard was never trashed by the ents.

Say Saruman gives more simple instructions that Merry and Pippin are to be taken alive, or the orcs just disobey and chop their legs off and eat them. The orcs are slaughtered by the Rohirrim and Merry and Pippin are killed in the confusion, Treebeard is never alerted to the destruction of the forests by Saruman, and the ents never launch an assault on the fortress.   


What might have changed in the war of the ring, especially in the Return of the King era?
gpt
For one thing, there would have been a lot more orcs at the siege of Minas Tirith. Saruman may have been able to forsee events and guide Sauron's armies to seriously weaken the armies of men, if not destroy them outright. Rohan may not have come to aid Gondor and things get pretty bleak. The ents would eventually find the destruction of their forest and would ultimately act as they did, if not a great deal of time later. It would almost certainly be too late to change much, even if they destroy isengard.

What happens before that is a good question. Sam and Frodo would probably still have cast the one ring into mount Doom, ending Sauron's reign before it began. Perhaps Minas Tirith and Rohan had fallen by that point, in which case, orcs and the surviving men would live in Saruman's empire not unlike what he accomplished in the Shire, but spanning across all of middle earth. The elves still nope the fuck out to the undying lands and the fourth age is a much darker one than it would otherwise have been.

If the siege of Minas Tirith still goes well for the humans, you probably have the forces of Gondor slaughtered at the black gate either by the forces of Mordor alone, or in a battle on two fronts; Mordor to the east and the uruks from the West. If the ring is captured, there is no real contest between Sauron and Saruman over it, as Saruman was never in a position to take it, and neither would share power. Perhaps before returning to Eru, Saruman would realize his folly, but it would be too late unless the Valar or Eru intervene directly.

Either way, it's not great. At best the shattered nations of men are ruled by the iron fist of the uruk and their master Saruman. At worst, Sauron wins and everything is a fucked to death pile of shit into which the greatest of the Maiar sews his own discordant notes of creation as had Melkor before him. Eru isn't happy, and maybe decides to start over without demigods to fuck things up.