The four powers governing Berlin ( France , the Soviet Union , the United Kingdom , and the United States ) had agreed at the 1945 Potsdam Conference that Allied personnel would not be stopped by East German police in any sector of Berlin . But on 22 October 1961 , just two months after the construction of the Wall , the US Chief of Mission in West Berlin , E. Allan Lightner , was stopped in his car ( which had occupation forces license plates ) while going to a theatre in East Berlin . Army General Lucius D. Clay ( Retired ) , U.S. President John F. Kennedy 's Special Advisor in West Berlin , decided to demonstrate American resolve
Potsdam Conference
Potsdam Conference
Cold War (1953–1962)