Let's learn about the Yalta and Postdam Conferences!
First, it started with the Yalta Conference. The countries involved were England, USA, and USSR.
During this conference, the countries involved decided to create NATO to help solve the current issues. They also decided to divide Germany into 4 parts.
After the Yalta Conference was the Postdam Conference. Churchill was replaced by Attlee and Roosevelt was replaced by Truman.
The leaders decided the specific zones that Germany would be divided into. They decided to divide Berlin into four zones as well.
Eventually, these zones led to the Iron Curtain, which "split" communist and capitalist countries. Even though in most parts it wasn't a physical curtain that separated the countries, it still caused a divided world.