Geopolitics is the study of the effects of Earth's geography on politics and international relations. Geopolitics usually refers to countries and relations between them. According to multiple researchers, the term is currently being used to describe a broad spectrum of concepts, in a general sense used as "a synonym for international political relations", but more specifically "to imply the global structure of such relations"; this usage builds on an "early-twentieth-century term for a pseudoscience of political geography" and other pseudoscientific theories of historical and geographic determinism.