The term Mesoamerica—literally, "middle America" in Greek—was first used by the German ethnologist Paul Kirchhoff, who noted that similarities existed among the various pre-Columbian cultures within the region that included southern Mexico, Guatemala, Belize, El Salvador, western Honduras, and the Pacific lowlands of Nicaragua and northwestern Costa Rica. In the tradition of cultural history, the prevalent archaeological theory of the early to middle 20th century, Kirchhoff defined this zone as a culture area based on a suite of interrelated cultural similarities brought about by millennia of inter- and intra-regional interaction (i.e., diffusion).