Question

Why is the Post WWII era known as the Cold War?

Answer 1

Because it was a kind of war where the two opponents (the US and the USSR) where not directly fighting each other on the battlefield (in a face to face confrontation of armies) but indirectly, covertly and apparently without casualties or destruction.

Explanation:

After WWII, and maybe even during it, the relation between the US and Stalin's USSR where not very good. Basically the two nations accepted each other as ally only to fight successfully against Hitler. Once Germany lost the war the two started immediately to antagonize each other (in particular about territories, areas of influence and politics).

They even divided the World in Blocks (Soviet and American controlled) with even an ideal barrier between them, The Iron Curtain.

The problem was that a direct and effective war between them was impractical for two big reasons:
1) People on both sides were tired of wars (after 2 World Wars);
2) Both had terrible nuclear weapons that would have destroyed (if used) both contenders.

So the two contenders fought a covert and indirect "Cold" war through "Hot" conflicts in other nations such as: Korea, Viet-Nam and Afghanistan (helping one nation or the other with weapons, logistic support or intelligence, for example).

Also they spent all the time aggressively spying each other and sabotaging one the activities of the other fomenting instability through civil unrest and coup d’états.