If the Incheon landings [0] had been a failure during the Korean War in 1950, it's hard to see how nuclear weapons wouldn't have been employed, especially as China was neither involved nor had their own.

And if they'd been normalized in a second war, even at tactical scale, it makes you wonder how the rest of nuclear history would have unfolded.

[0] https://en.m.wikipedia.org/wiki/Battle_of_Inchon