A world-system is a socioeconomic system, under systems theory, that encompasses part or all of the globe, detailing the aggregate structural result of the sum of the interactions between polities. World-systems are usually larger than single states, but do not have to be global. The Westphalian System is the preeminent world-system operating in the contemporary world, denoting the system of sovereign states and nation-states produced by the Westphalian Treaties in 1648. Several world-systems can coexist, provided that they have little or no interaction with one another. Where such interactions becomes significant, separate world-systems merge into a new, larger world-system. Through the process of globalization, the modern world has reached the state of one dominant world-system, but in human history there have been periods where separate world-systems existed simultaneously, according to Janet Abu-Lughod. The most well-known version of the world-system approach has been developed by Immanuel Wallerstein. A world-system is a crucial element of the world-system theory, a multidisciplinary, macro-scale approach to world history and social change.