In the 1969 election, the SPD—headed by Willy Brandt—gained enough votes to form a coalition government with the FDP. Although Chancellor for only just over four years, Brandt was one of the most popular politicians in the whole period. Brandt was a gifted speaker and the growth of the Social Democrats from there on was in no small part due to his personality. Brandt began a policy of rapprochement with West Germany's eastern neighbors known as "Ostpolitik", a policy opposed by the CDU. The issue of improving relations with Poland, Czechoslovakia, and East Germany made for an increasingly aggressive tone in public debates but it was a huge step forward when Willy Brandt and the Foreign Minister, Walther Scheel (FDP) negotiated agreements with all three countries (Moscow Agreement, August 1970, Warsaw Agreement, December 1970, Four-Power Agreement over the status of West Berlin in 1971 and an agreement on relations between West and East Germany, signed in December 1972). These agreements were the basis for a rapid improvement in the relations between east and west and led, in the long term, to the dismantlement of the Warsaw Treaty and the Soviet Union's control over East-Central Europe. During a visit to Warsaw on 7 December 1970, Brandt made the Warschauer Kniefall by kneeling before a monument to those killed in the Warsaw Ghetto Uprising, a gesture of humility and penance that no German Chancellor had made until that time. Chancellor Brandt was forced to resign in May 1974, after Günter Guillaume, a senior member of his staff, was uncovered as a spy for the East German intelligence service, the Stasi. Brandt's contributions to world peace led to his winning the Nobel Peace Prize for 1971.