Avengers: Endgame - Everything That Changes If The Heroes Steal The Infinity Stones From The Past

8. Ultron Wins (Or At Least Escapes)

It wouldn't be entirely fair to claim that Tony Stark wouldn't have made Ultron without Scarlet Witch inspiring his fear of the end of the universe, because he was probably already suffering PTSD before the Battle Of New York thanks to his kidnapping and near death in Afghanistan.

At the outset of Age Of Ultron, Tony has already developed the drone army that ends up being the precursor to Ultron's infected army, too, so his intention to protect Earth through dangerous technological over-reaching was already implanted in his mind. In other words, he was already Frankenstein and his monster would have been born either way (it's not like Bruce Banner has the same vision and he still helps build Ultron).

But without the Stones, Ultron's story would have been very different. He probably wouldn't have recruited the Twins (since they wouldn't be empowered) and they couldn't have turned on him. They weren't necessarily key to the Avengers' victory over Ultron, but Vision certainly was and without him to deal the killer blow to the robo-villain, he could have escaped in his final drone body to rebuild once more.

Even ignoring Vision's part at the end of things, three fewer heroes could have swung the tide for Ultron in the Battle Of Sokovia too. There's just no saying that it would be the same.