The establishment of diplomatic ties with West Germany did not alter the PCR position on the existence of two German states. Each country, at the time the diplomatic exchange was made public, simply reasserted its own positions: the West German government reiterated its right and obligation to speak for the entire German people, and the Bucharest government asserted that one of the fundamental realities of the post-World War II era "is the existence of two German states." Although Romania reaffirmed the existence of East Germany as a separate state, it did not make recognition of the East German regime by West Germany a precondition for the establishment of diplomatic relations with the West German government. The East German regime was highly critical of the Romanian establishment of relations with West Germany, and there followed a serious decline in Romanian-East German relations. PCR leaders responded to East German criticisms by declaring that "the foreign policy of a socialist state is laid down by the party and the government of the country in question and they need render account only to their people." In the period since 1967 relations with West Germany have continued without major difficulties. Although the Ceausescu regime has not hesitated to criticize elements of German policy with which it does not agree, the two governments have sought to minimize differences in ideology and in foreign and domestic policies in the interest of maintaining good relations. In economic exchanges between the two countries Romania has had a continuous balance of trade deficit, a situation that both countries were attempting to correct. In mid-1970 Prime Minister Maurer paid an official visit to Bonn, becoming the first Eastern European head of government to do so. In May 1971 the West German government reciprocated, President Gustav Heinemann making a state visit to Romania. The United States Relations with the United States were initiated on a limited scale in the early 1960s, and ambassadors were exchanged in 1964, but relations declined with the increasing United States role in the Republic of Vietnam (South Vietnam). After the opening of the Paris peace talks and particularly after the Warsaw Pact invasion of Czechoslovakia that same year, relations between the two states improved significantly. Trade relations remained minimal, however, partly because of United States legal restrictions on trade with Eastern European countries. The improved relations between the two nations were demonstrated by the visit of President Nixon to Romania in August 1969, marking the first visit of a United States head of state to a communist country since the 1945 Yalta Conference. Press reports indicated that the president received an enthusiastic welcome from the Romanian people and that in meetings with Ceausescu a wide range of international problems were discussed.