Yes, generally speaking it is true that the European Union was established so european nations could trade together without so many restrictions, since they all united under a single currency.
One of the reasons, among few others, for the formation of the European Union was so that the nation members can trade freely between each other without restrictions. This was a big goal of the European Union because it was something that was enabling the economies of the country members to prosper and grow, as well as to start and support each other, and go out on the global market as a unified economies in order to be more competitive and more profitable.
The US constitution is broad and needs to cover every state. States can make their constitution more specific for their needs and explain everything in more detail
