This document summarizes Immanuel Wallerstein's world-systems theory, which divides the world into three categories: the core, semi-periphery, and periphery. It states that Wallerstein viewed the world as a single global economy in the 1400s-1600s. Examples are provided of different countries' placement within this system, such as England in the core and Poland in the periphery. Both strengths and weaknesses of the theory are discussed, such as its inability to categorize all countries and changing applicability over time.