Check out this link, and run your mouse over the graphic to see the missing connection. I commend the entire page to your attention.
Understanding Economics: Context of This Course.
Inside the back cover of the 17th edition of Economics by Samuelson & Nordhaus there is a "Family Tree of Economics" that graphically summarizes the major trends in the discipline's modern history. It presents the most famous exponents of the main schools of economic thought: Mercantilism, the Physiocrats, the Classical School and Neoclassical Economics -- leading to the two modern "endpoints" of Modern Mainstream Economics and Socialism. The book's chart depicts the "value-free" science of economics in a rather partisan way: it places Modern Mainstream Economics center stage as the fulfillment of its precursors -- and leaves Socialism on the far left, trailing off into irrelevance.