Why was the United States so determined to help West Berlin when it had no real interest to protect it there

The United States supported West Berlin because they wanted to stop the spread of communism. The system at the time was called “Containment” in this system communist nations could keep hold of the land they were not allowed to spread. The Berlin Wall was built to keep people from Communist controlled East Berlin from escaping to West Berlin. The U.S supported West Berlin because they were fighting to resist communist, by supporting them the U.S hoped to ensure communists would not gain control of West Berlin.