Why did the European community rename to the European union?

Since it was founded in 1957, the organisation has had several names. Before the European Union, it had been known as the European Community. It started mainly to work for economic ties, but as its aims have changed and extended into a broader range of issues, the name has been changed to fit that. It is now far from being just purely about economic issues, so the name European Economic Community would not really fit. Many organisations change their names as they develop. That is how the EEC went to being the EC and now EU.