Geopolitics is the study of the relationships between geography, politics, and power. It examines how the physical and human geography of the world influences the distribution of power and the relationships between states and other actors. Geopoliticians look at the ways in which geographical factors such as natural resources, geographic location, and population demographics shape political relationships and international affairs. They also consider how political decisions and actions impact geographical factors, such as through the creation of borders or the exploitation of resources.
Source: Haass, R. N. (1997). The Reluctant Sheriff: The United States After the Cold War. Council on Foreign Relations Press.