Nuclear war has been mentioned a couple times but i feel it deserves elaboration: We’ve been real fucking close a couple times. There was a Soviet “nuclear counterattack station”, or whatever, that got the “nuclear strike detected, fire retaliatory missiles” signal and the person responsible simply refused. The signal was due to a glitch, there was no attack. That guy probably saved millions and millions of lives by refusing to carry out his duty.

If you consider (potential) timelines being “close” to ours in terms of only a small number of things needing to change to get us there, the one where everything went to nuclear hell is very close to ours–but we’re not in that one.