Economist Fritz Machlup traces the origin of the term 'economic integration' to a group of five economists writing in the 1940s, including Wilhelm Röpke, Ludwig von Mises and Friedrich von Hayek. Economic integration was a foundational plank of US foreign policy after World War II.
The degree of economic integration can be categorized into six stages:
Economic integration also tends to precede political integration. In fact, Balassa believed that supranational common markets, with their free movement of economic factors across national borders, naturally generate demand for further integration, not only economically (via monetary unions) but also politically--and, thus, that economic communities naturally evolve into political unions over time.