The world systems theory, which was established by sociologist Immanuel Wallerstein, is an approach to world history and social change that suggests there is a world economic system in which some countries benefit while others are exploited. This theory emphasizes the social structure of global inequality. World-systems theory was aiming to replace modernization theory, which Wallerstein criticized for three reasons: its focus on the nation state as the only unit of analysis, its assumption that there is only a single path of evolutionary development for all countries and its disregard of transnational structures that constrain local and national development.
The world system theory is correct because in many of the world countries, there is economic inequality where by some countries are beneficiaries of economic system while others are exploited. World-Systems Theory can be useful in understanding world history and the core countries' motives for imperialization and other involvements like the US aid following natural disasters in developing Central American countries or imposing regimes on other core states.