So here’s the scenario to test it. I dunno if you’ve seen the godawful film Superman IV (if you haven’t, don’t). The plot is Superman decides to rid the world of nuclear weapons.
All existing nuclear warheads from any nuclear power are flung into the sun, as are any new ones that have been built. The film was made in 1987, the tail end of the Cold War. With no MAD deterrence left, what are the chances that a conventional World War III occurs as a result of this universal nuclear disarmament?
As long as Superman is still around, he remains a deterrent against conventional war - I’d expect him to seriously impede a tank invasion of Western Europe for example. The real problem would be other WMDs like poison gas or biological weapons.
Read Watchmen; one of the end-of-comic fillers was a magazine article in which the writer postulated that if the Soviets emptied their silos at the US all at once, Manhattan would not be able to stop more than about half, and if the US continued in its prideful arrogance on the assumption that the Soviets daren’t do anything about it, Armageddon was not far away.
Except it wasn’t true, even in Watchmen. In the comic, the US projected (and Manhattan seemed to agree) that in the event of a full-scale exchange of nukes, Manhattan would not be able to keep even half the Russian missiles (presumably coming from multiple directions) from hitting their targets.
ET: I see the Martian beat me to this by 12 hours.
Yeah, that’s more or less why I answered as I did above. To elaborate: the Superman of the Superman through Superman IV can’t stop a nuclear war - he has a hard enough time stopping two missiles in the first movie (it requires an extraordinary effort), and eliminating all the nuclear weapons in Superman IV is another indication that he thinks that he can’t stop an all out nuclear exchange. Superman can seriously impede (and thus can deter) a conventional war of just about any size though (massed tanks heading from Warsaw to Paris are not going to make it if Superman is around). Superman does need to worry about biological warfare and chemical warfare - and after eliminating nuclear weapons he ought to work on those. In the post-nuclear (and post-other WMD) world that Superman creates, nations do need to worry about massive conventional attack if Superman suddenly becomes unavailable, but the prospects for an immediate WWIII after Superman ends all WMDs are pretty slight.