Its started after World War 2 because after a lot of issues arose between the US and USSR. They had a mutual distrust with each other stemming from the way the US had perceived the USSR as an illegitimate part of the international community. The way the USSR perceived the US as people who intervened in everyone's business and had amounted weapons.
The puppy no longer greetng Molly when she enters the house is an example of extinction. This is because the puppy lacks motivation to greet her when she enters the house because she does not have treats.
