How did nuclear weapons make it a cold war?

At the heart of the Cold War and the development of nuclear weapons lay the concept of "Mutually Assured Destruction, fittingly shortened to MAD.

The meaning of this was that both sides had so much weaponry that it was impossible to knock the enemy out completely with the first blow.

And if you didn't manage that, the revenge would damage your countrybeyond what was considered acceptable.

So it was called a "cold" war, because while it never broke out into a real war, both sides kept preparing and posing as if it MIGHT happen.