Mutual Assured Destruction prevented nuclear war for the duration of the Cold War.
Even during the Cuban Missile Crisis the Soviets realized that it was Fidel Castro who was screaming “Let’s you and them fight!!”. Cooler heads prevailed.
After all, if you’re communist & atheistic, this life is all there is.
Russians aren’t suicidal. Putin has no assurance of 100% success & total interdiction of a U.S. second strike. His new weapons systems are mainly for intimidation, because as Nikita Khrushchev once said, “If we fire all our rockets at America, then they have completely FAILED in their purpose!”
But Muslims are suicidal, because their religion tells them only shahids have a direct path to paradise. Even so the mullahs in Iran despite their bluster aren’t in that big a hurry to go nuclear; not with Israeli nukes aimed at them like a cocked pistol.
Ditto the Pakistanis, with an equally nuclear India watching them like a hawk.
I believe that was actually Che Guevara who said that, and even Castro was appalled, one of the reasons that Fidel didn't shed a tear when Che got his in Bolivia.