Why did president Johnson believe that it was important for the United states to win in Vietnam?

The United States had been involved in Vietnam since the 1950's and was part of the philosophy that communism must be contained in Southeast Asia. Kennedy had decided before his death he was going to look for a method to get out of Vietnam, but LBJ was from the "old school " war hawk philosophy of containment so he expanded the war and believed that the United States had to win to stop communism.