Okay kiddo, so there was a time when two big countries, the United States and the Soviet Union, didn't get along. They were both really strong and didn't like each other's ideas about how to run things. This disagreement caused a lot of tension between them and they were always kind of fighting with each other, but not really in a physical way.
This time period is called the Cold War, because while they didn't have big battles and shoot at each other, they were in a constant state of disagreement and they were both always ready to fight if the other one did something they didn't like. No bullets were fired, but it was like they were both getting ready for a big fight... just in case.
So, from 1985 to 1991, this disagreement was still going on. A guy named Mikhail Gorbachev was in charge of the Soviet Union, and he wanted to make some changes to how things were done there. He was interested in making the country more modern and making changes that would make it better for the people who lived there.
But, the United States and the Soviet Union still didn't trust each other. They thought the other one might be up to something bad, so they both kept their armies and weapons ready, just in case.
Then, something pretty big happened in 1989. The Berlin Wall, which was a symbol of the split between the two sides, came down. People got to run across the border and reunite with their families and friends who were on the other side. It was a pretty big moment in history.
After this, the Soviet Union started to fall apart. The different republics that made up the Union started to declare independence and wanted to be their own countries. This caused a lot of problems, but eventually, in 1991, the Soviet Union officially ended. The Cold War was over.
So, in short, the Cold War was a time when two big countries, the United States and the Soviet Union, didn't get along and were always ready for a fight, but they never actually fought. This disagreement lasted from 1985 to 1991, when the Soviet Union fell apart and the Cold War officially ended.