The Cold War is not used to describe a war in the classic sense, but rather a tense world situation that had a decisive impact on world history, initially between 1945 and 1991. At its core were two opposing military alliances that utilised different social systems: on the one hand, the Western community of states (westliche Staatengemeinschaft) under the leadership of the United States, which came together in the North Atlantic Treaty Organization (NATO) in 1949; on the other hand, the socialist community of states (sozialistische Staatengemeinschaft), which was constituted in 1955 as the Warsaw Treaty States in response to the founding of NATO. Both military alliances were open rivals on the world stage. Initial tensions had already arisen during the blockade of the western part of Berlin by the Soviet Union in 1948/49. Although the war was initially understood to be cold in the sense that the weapons of NATO and the Warsaw Pact (Warschauer Pakt) did not directly heat up, i. e. military power was not used directly, this rivalry determined a whole series of so-called proxy wars, such as the Korean War (1950/53) and the Vietnam War (1955/75). The founding of the GDR in October 1949 was characterised by emerging tensions between these still-forming communities of states and took place in clear distinction from the military alliances of West-Germany. A dividing line - also known as the iron curtain - ran through Europe between Western-allied and socialist states. This dividing line was legally defined by West Germany as the inner-German border in state-divided Germany, then materialised physically from 1961 in the form of militarily secured barriers known as the Wall (Mauer), which the GDR erected along its western state border (Staatsgrenze West). Systemic competition between the communities of states and social systems also characterised domestic GDR politics.