Geopolitik is a branch of 19th-century German statecraft, foreign policy and geostrategy. It developed from the writings of various German philosophers, geographers and thinkers, including Oswald Spengler (1880-1936), Alexander Humboldt (1769-1859), Karl Ritter (1779-1859), Friedrich Ratzel (1844-1904), the Swede Rudolf Kjellén (1864-1922), and Karl Haushofer (1869-1946). The ideology of Adolf Hitler adapted, and eventually incorporated some of its tenets.