"India and Pakistan at each others throats and both have nukes
when have nuclear weapons deterred a war?"
Confrontation between India & Pakistan post-becoming nuclear armed can be described as small scale skirmishes at best.
Have a look at the death tolls from the Partition & '71 Pakistani / (what's now known as ) Bangladeshi / Indian war if you want to see what "at each others throats" looks like without nuclear deterrent.
Nuclear deterrent in this specific scenario has capped the level of escalation to skirmish level.
"Russia threatening to use tactical nuclear weapons"
But they haven't yet. Russia also hasn't attacked any NATO countries on their borders due to, for example, the Baltics sitting under the NATO/nuclear umbrella.
If you want to know what conflict may have looked like without nuclear deterrent, see WWI & WW2.
Since WW2 conflicts have been regional, and really not involving direct confrontation between major players.
"yes all it takes is one idiot simple enough to press the Big Red Button."
That's why Iran can't be allowed to obtain nuclear weaponry and siphon it off to their non-State actors (Hamas, Hezbollah, Houthis, Iraqi militias, other terror groups). Glad we agree.
