His geopolitics professor was Karl Haushofer, a former general in the German Army who was a proponent of the concept of Lebensraum ("living space"), which Haushofer cited to justify the proposal that Germany should forcefully conquer additional territory in Eastern Europe.[17][14] Hess later introduced this concept to Adolf Hitler, and it became one of the pillars of Nazi Party ideology.[15][18] Hess became friends with Haushofer and his son Albrecht, a social theorist and lecturer.[14]