The article demonstrates the dynamism of Inter-Korean relations in 1950s-1980s as well as its domestic and foreign factors. It systemically evaluates on bilateral treaties between the United States and South Korea, the United States and Japan, and Japan and South Korea, on one hand, and between the Soviet Union and North Korea, and the Chinese People’s Republic and North Korea, on other hand. It highlights the formation of a regional sub-system of international relations and its influence on Inter-Korean relations. Emphasis is given to various concepts of unification of the Korean Peninsula, which emerged during that period. Attention is given to transformation of those concepts thanks to both domestic developments in either of the Koreas and developments taking place in the region in general. The article pays special attention to domestic and foreign factors of the Inter-Korean rapprochement of 1972, provides with analysis of basic principles of the Joint Declaration between the North and the South, as well as of the differences in perception of the Joint Declaration in the Korean People’s Democratic Republic and in the Republic of Korea. The authors demonstrate how end of the War in Vietnam influenced growing tensions on the Korean Peninsula in late 1970s. They pay attention to the debate on possible withdrawal of U.S. troops from the Korean Peninsula, which took place in late 1970s. They evaluate on domestic changes in the United States, the Chinese People’s Republic and the Republic of Korea, which were results of domestic leadership change, and which significantly influenced on foreign policies of corresponding countries, including their policies towards the Korean Peninsula. The article concludes that the short period of Inter-Korean rapprochement came to an end, while new period of growing tensions on the Korean Peninsula began.