Which theory divides nations into four groups including core nations and periphery nations?

The theory that divides nations into core, semi-periphery, and periphery nations is known as World-Systems Theory, developed by sociologist Immanuel Wallerstein. Core nations are economically dominant and technologically advanced, while peripheral nations are less developed and often exploited for resources. Semi-peripheral nations fall in between, exhibiting characteristics of both core and peripheral countries. This framework helps to analyze global inequalities and the dynamics of economic and political power.