Geopolitics is a method of political analysis, popular in Central Europe during the first half of the 20th century, that emphasized the role played by geography in international relations. Geopolitical theorists stress that natural political boundaries and access to important waterways are vital to a nation's survival. The term was first used (1916) by Rudolf Kjellen, a Swedish political scientist, and was later borrowed by Karl Haushofer, a German geographer and follower of Friedrich Ratzel. Haushofer founded (1922) the Institute of Geopolitics in Munich, from which he proceeded to publicize geopolitical ideas, including Sir Walford J. Mackinder's theory of an Eurasian “heartland” central to world domination. Haushofer's writings found favor with the Nazi leadership, and his ideas were used to justify German expansion during the Nazi era. Many expansionist justifications, including the American “manifest destiny” as well as the German Lebensraum, are based on geopolitical considerations.