In Cold War times, we had in Germany the so-called "Hallstein doctrine" :
A basic foreign policy principle of the Government of the Federal Republic of Germany from 1955 to 1969. According to this doctrine, the Federal Republic asserted the exclusive right to represent the entire German nation (Alleinvertretungsanspruch). It did not establish or maintain diplomatic relations with states that recognize the German Democratic Republic (DDR). (Exception: The USSR, as one of the victorious powers of World War II.) The doctrine is applied for the first time against Yugoslavia (1957), followed by Cuba (1963) and Arab countries (1965).
Even at those times, we could go everywhere - I've been in the GDR and East Berlin three times in the above mentioned period (one time with the Conservative Youth

).