Silly communists, Atomics are for Capitalists.
At the end of World War II, the already paranoid Stalin found himself outflanked. Disagreements ranging from the treatment of the defeated, the belated opening of the second front, and the atomic questions caused conflict between "Uncle Joe" (All families need a creepy uncle) and the capitalist powers.
This led to a situation similar to two bickering toddlers. The Marshall Plan, which left Russia in a no-win situation coupled with the Iron curtain were two moves made early by the US. What did the Communists do in return? The Berlin Blockade and extension of Communism into Czechoslovakia.
Mao adored Stalin. Stalin thought Mao was dumb. Mao eventually got smart. (But not before he caused huge famines and killed millions of his people.)
During the Cold War, Mao increased China's power as a player in the war. His specialty was throwing a monkey wrench in already malfunctioning political realtions between the communists and the capitalists. He constantly antagonized the US by threats of attacking Taiwan, where the non-communist Chinese had fled to.
He listened to one too many of Stalin's ideas, one including an amazing russian crop technique. (Which by the way caused massive famine when it failed)
Then there was that one time to save the crops, peasants had to stand for hours banging on pots to scare away and kill the small birds that were destroying the crops. Great move Mao. He killed lots of small birds...the ones that ate the insects that were REALLY eating crops. Go more famine.
The Communist people threw a fit. Of course open rebellion ended in death, so there were a few martyrs by the end.
The Berlin wall failed. The smaller communist countries refused to keep up the barbed wire fences that were in places that was not the Berlin wall. One these became run down and a safety issue they were removed. Leaving the Berlin wall a random strip of wall that could be avoided by leaving from one of the many other unwalled areas. It was dismantled.
Shortly afterwards, so was the USSR.
The USSR dissolved ITSELF with a treaty.