Answer:
Since the 1930s, four macroeconomic theories have been proposed: Keynesian economics, monetarism, the new classical economics, and supply-side economics. All these theories are based, in varying degrees, on the classical economics that preceded the advent of Keynesian economics in the 1930s. Smith argued against mercantilism and was a major proponent of laissez-faire economic policies. In his first book, "The Theory of Moral Sentiments," Smith proposed the idea of an invisible hand—the tendency of free markets to regulate themselves by means of competition, supply and demand, and self-interest.