The world-systems theory stresses that world-systems (and not nation states) should be the basic unit of social analysis. The last temporal feature is the crisis: a crisis occurs, if a constellation of circumstances brings about the end of the system. For example, the problem of underconsumption, wherein the drive-down of wages increases the profit for the capitalists on the short-run, but considering the long run, the decreasing of wages may have a crucially harmful effect by reducing the demand for the product. The term contradiction means a general controversy in the system, usually concerning some short term vs. Cyclical rhythms represent the short-term fluctuation of economy, while secular trends mean deeper long run tendencies, such as general economic growth or decline. World-systems, past world-systems and the modern world-system, have temporal features. Resources are redistributed from the underdeveloped, typically raw materials-exporting, poor part of the world (the periphery) to developed, industrialized core. Countries tend to fall into one or another of these interdependent zones core countries, semi-periphery countries and the periphery countries. In the modern world-system, the division of labor consists of three zones according to the prevalence of profitable industries or activities: core, semiperiphery, and periphery. The modern world-system has a multi-state political structure (the interstate system) and therefore its division of labor is international division of labor. World-systems are defined by the existence of a division of labor. A world-system is a crucial element of the world-system theory, a multidisciplinary, macro-scale approach to world history and social change. The most well-known version of the world-system approach has been developed by Immanuel Wallerstein. 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. Where such interactions becomes significant, separate world-systems merge into a new, larger world-system. Several world-systems can coexist, provided that they have little or no interaction with one another. 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. World-systems are usually larger than single states, but do not have to be global. 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.