Comment by skissane

The EU in many ways acts like one big economy due to its customs union, freedom of movement of workers, capital, goods and services, extensive harmonised regulations, partially harmonised taxation, wealth transfers between members, a common currency to a substantial part of it, etc. It is a lot more tightly integrated than some mere 28 member free trade area would be, although still not as tightly integrated as say the 50 states of the US are. (And the 50 US states all have distinct economies from each other, with sectors that are big in one state being small or even non-existent in another.)