> but history tells us that the most likely trigger for it happening would've been human or machine error, not some attempt at empire expansion
I think you're falling victim to the post hoc fallacy to some degree. Remember that the Cold War ended up only lasting about 4 decades or so, which limited the amount of time for incidents to occur that could have led to WWIII. Also remember that the process of succession of the leadership of the USSR was a very convoluted one. Most Soviet leaders remained in office until they died, which meant that a succession could occur at any moment, possibly even during a period where unusual things were happening with the party which might get sorted out quickly but could result in someone seizing power who might otherwise not had the chance. Also remember that dirty politics and coups were rampant in the communist sphere of influence and there is little reason to assume those tactics would not be used at home (as indeed they were). Especially considering the unsuccessful coup against Gorbachev. Given these things it's safe to say that there was absolutely no significant guarantee that the leader of the Soviet Union could be expected to be reasonable in any way. As indeed the example of Stalin plainly shows.
It's immanently possible both that the Cold War could have extended several years if not decades longer and an aggressive political figure akin to Stalin could have taken control of the Soviet Union almost at any point during its history.
Given these facts the idea that a pre-emptive nuclear strike from the Soviets could have occurred at any time during the Cold War was not as far fetched as we in the present, having avoided such a calamity, should assume. All it would have taken was the death of the General Secretary at an inopportune time and some sort of fight for supremacy within the party married with some sort of geopolitical state of high tension and a firebrand Soviet leader who ends up in control of a sufficient part of the armed forces (or perhaps all of them).
Here's two times we came close. They're both stories of Russians deciding not to pull the trigger based on faulty data, but I would not be surprised if there's a couple stories floating around of Americans making the same decision. It didn't need aggressive heads of state to happen at all.
I think you're falling victim to the post hoc fallacy to some degree. Remember that the Cold War ended up only lasting about 4 decades or so, which limited the amount of time for incidents to occur that could have led to WWIII. Also remember that the process of succession of the leadership of the USSR was a very convoluted one. Most Soviet leaders remained in office until they died, which meant that a succession could occur at any moment, possibly even during a period where unusual things were happening with the party which might get sorted out quickly but could result in someone seizing power who might otherwise not had the chance. Also remember that dirty politics and coups were rampant in the communist sphere of influence and there is little reason to assume those tactics would not be used at home (as indeed they were). Especially considering the unsuccessful coup against Gorbachev. Given these things it's safe to say that there was absolutely no significant guarantee that the leader of the Soviet Union could be expected to be reasonable in any way. As indeed the example of Stalin plainly shows.
It's immanently possible both that the Cold War could have extended several years if not decades longer and an aggressive political figure akin to Stalin could have taken control of the Soviet Union almost at any point during its history.
Given these facts the idea that a pre-emptive nuclear strike from the Soviets could have occurred at any time during the Cold War was not as far fetched as we in the present, having avoided such a calamity, should assume. All it would have taken was the death of the General Secretary at an inopportune time and some sort of fight for supremacy within the party married with some sort of geopolitical state of high tension and a firebrand Soviet leader who ends up in control of a sufficient part of the armed forces (or perhaps all of them).