The idea of containment was brought on by George Kennan's Long Telegram sent from the US embassy in the Soviet Union (modern day Russia) back to the US. He warned that the Soviet Union and their ideas of communism needed to be stopped so he came up with the idea of containment. The U.S. implemented this policy pretty well as they fought the Korean War to stop North Korea from invading South Korea and making Korea a communist country. They didn't lessen the spread of communism in this sitation, they simply contained it. However, while so called Cold War lasted for multiple decades, the ideas of Communism did not spread much further than they started before this policy was put into place.
Economic distress and resentment of the treaty within Germany helped fuel the ultra-nationalist sentiment that led to the rise of Adolf Hitler and his Nazi Party, as well as the coming of a World War II just two decades later.
