It was the fact that world super powers at the time (U.S) and (U.S.S.R) where building up an armory of nukes but they both knew if they where to use these weapons it would utterly destroy the world.
Here's a memory aid: (U.S): hey Russia lets not kill each other with nukes in this war lets just keep it "COOL" and spy on each other instead
Answer:
go to this link
Explanation:
https://www.csmonitor.com/1991/0328/28191.html
I have experiences this in my own life when I join my schools reading Olympics team and we all had to learn an part of each book we were given because if one of us didn't have the answer we needed to be able to help each other out
The 1st one i think, but i don't know. sorry