Final answer:
The differences relate to levels of economic integration: free trade associations permit trade without duties among members, common markets add shared external trade policies, and economic unions also coordinate fiscal and monetary policies.
Step-by-step explanation:
The difference between a free trade association, a common market, and an economic union lies in the level of integration and cooperation among member countries. A free trade association offers free trade in goods between its members while allowing each country to determine its own external trade policy. In contrast, a common market involves not only free trade within the group but also requires a shared external trade policy. An economic union is an advanced stage that encompasses all the features of a common market with the added coordination of fiscal and monetary policy between member countries. A prominent example is the European Union (EU), which started as a free trade association, developed into a common market, and eventually became an economic union with a common currency, the euro, and other integrated policies to facilitate the free movement of goods, labor, and capital.