Nuclear Deterrence and Nuclear Proliferation

What is the difference between nuclear deterrence and nuclear proliferation? Explain the key elements of successful nuclear deterrence. Why was nuclear deterrence effective during the Cold War? If it worked for the U.S. and Soviet Union during that period, is it a viable option for nations today? Not looking for any lengthy response or anything, any information would be helpful, god bless.

Nuclear proliferation is the spread of nuclear weapons. Nuclear deterrence is the theory that when two nations have the same firepower and understand that using their weapons will surely generate a response as, or more damaging than theirs, that understanding will keep them from being used. It worked in the cold war partly by effictiveness and partly luck. It was tested at the height of the Cuban Missle Crisis and did it's intended job.

The downside for today's world is it's just a theory and has little room for error like misunderstandings or an insane person with their finger on the trigger.