Classical economics
Adam Smith's book The Wealth of Nations (1776) was the beginning of classical economics. Smith said that if everyone did what was best for themselves, the result would be best for society. Before that, economics was about the king's personal interests, and the wealth of a nation was measured by the king's treasury. Smith said what's important is what's best for the whole nation, and that wealth should be measured by the yearly income of the nation. He wanted to discover how wealth can grow, and how people could do things to support that growth. Smith's book said land, labor, and capital were the three "factors of production" and the main contributors to a nation's wealth.