The main thesis of "The Wealth of Nations," written by Adam Smith in 1776, centers around the idea of free market economics and the benefits of capitalism. Smith argued that individuals acting in their self-interest inadvertently contribute to the economic well-being of society as a whole, a concept he famously termed "the invisible hand." He emphasized the importance of division of labor, competition, and the role of government in supporting rather than interfering with economic activity. Smith's work laid the foundation for modern economic theory, advocating for limited government intervention and the idea that markets function best when left to their own devices.