Much Cold War espionage and counter-espionage took place in Berlin, against a backdrop of potential superpower confrontation in which both sides had nuclear weapons set for a range that could hit Germany. In 1971, the Four-Power Agreement on Berlin was signed. While the Soviet Union applied the oversight of the four powers only to West Berlin, the Western Allies emphasized in a 1975 note to the United Nations their position that four-power oversight applied to Berlin as a whole. The agreement guaranteed access across East Germany to West Berlin and ended the potential for harassment or closure of the routes.