Following Adolf Hitler's rise to power, Lebensraum became an ideological principle of Nazism and provided justification for the German territorial expansion into East-Central Europe. The Nazi Generalplan Ost policy (the Master Plan for the East) was based on its tenets. It stipulated that most of the indigenous populations of Eastern Europe would have to be removed permanently (either through mass deportation to Siberia, death, or enslavement) including Polish, Ukrainian, Russian, and other Slavic nations considered racially inferior and non-Aryan. The Nazi government aimed at repopulating these lands with Germanic colonists in the name of Lebensraum during World War II and thereafter. The entire indigenous populations were to be decimated by starvation, allowing for their own agricultural surplus to feed Germany.
Hitler's strategic program for world domination was based on the belief in the power of Lebensraum, pursued by a racially superior society. People deemed to be part of inferior races, within the territory of Lebensraum expansion, were subjected to expulsion or destruction. The eugenics of Lebensraum assumed the right of the German Aryan master race (Herrenvolk) to remove indigenous people they considered to be of inferior racial stock (Untermenschen) in the name of their own living space. Nazi Germany also supported other "Aryan' nations" pursuing their own Lebensraum, including Fascist Italy's spazio vitale.
In the 19th century, the term Lebensraum was used by the German biologist, Oscar Peschel, in his 1860 review of Charles Darwin's Origins of Species (1859). In 1897, the ethnographer and geographer Friedrich Ratzel in his book Politische Geographie applied the word Lebensraum ("living space") to describe physical geography as a factor that influences human activities in developing into a society. In 1901, Ratzel extended his thesis in his essay titled "Lebensraum".
During World War I, the British blockade of trade to Germany caused food shortages in Germany and resources from Germany's African colonies were unable to help; this caused support to rise during the war for a Lebensraum that would expand Germany eastward into Russia to gain control of resources to stop the food shortages. In the period between the First and the Second world wars (1919–39) German nationalists adopted the term Lebensraum to their politics for the establishment of a Germanic colonial-empire like the British Empire, the French Empire, and the empire that the U.S. established with the westward expansion of the "American frontier", which was advocated and justified by the ideology of Manifest Destiny (1845). Ratzel said that the development of a people into a society was primarily influenced by their geographic situation (habitat), and that a society who successfully adapted to one geographic territory would naturally and logically expand the boundaries of their nation into another territory. Yet, to resolve German overpopulation, Ratzel said that Imperial Germany (1871–1918) required overseas colonies to which surplus Germans ought to emigrate.
In the event, Friedrich Ratzel's metaphoric concept of society as an organism — which grows and shrinks in logical relation to its Lebensraum (habitat) — proved especially influential upon the Swedish political scientist and conservative politician Johan Rudolf Kjellén (1864–1922) who interpreted that biological metaphor as a geopolitical natural-law. In the political monograph Schweden (1917; Sweden), Kjellén coined the terms geopolitik (the conditions and problems of a state that arise from its geographic territory), œcopolitik (the economic factors that affect the power of the state), and demopolitik (the social problems that arise from the racial composition of the state) to explain the political particulars to be considered for the successful administration and governing of a state. Moreover, he had great intellectual influence upon the politics of Imperial Germany, especially with Staten som livsform (1916; The State as a Life-form) an earlier political-science book read by the society of Imperial Germany, for whom the concept of geopolitik acquired an ideological definition unlike the original, human-geography definition.