Why was Germany split during the cold war?

The split happened at the end of WW2. When Berlin fell the first to arrive were the Soviet troops and then the Allied troops came into the city. The major parties decided to divide the city into four sections. There was the Eastern section overseen by Russia and then the 3 sections controlled by the Allies. This soon divided the city. When a border was created at the Eastern and Western section it further divided Germany. Finally, the Berlin Wall was built by Russia that further made the border between West Germany and East Germany solid. It came to represent the differences in governments, communism, and democracy and it stayed that way for 60 years with armies facing each other until 1989 when the wall came down.