Were there any wars that started before the first World war, but ended after? Because technically, The quote doesn’t say it prevented wars, just ended them.

You could make a strong case that the second world war came close though.

We’ve never seen warfare on that scale before, where one group of allies is fighting another, the closest is Ukraine, where two countries each have allies supplying weapons and other supplies.

OOTL - What show is this?

After the 2nd world war, we said surely this is the last big one, with understanding that ww4 would be fought with sticks and stones.

we might have thought nazi ideology would be gone too, but we decided to cognitively coherently separate pro US/NATO nazis from anti-NATO nazis, chasing ghosts of communism and warmongering towards nuclear powers became the cool thing again so easily.