system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The European Union (EU). What is it, and what does it mean to be part of it?

Assume I'm starting with almost no information, as I am not European and don't have much understanding of these matters.  Pros/cons also welcome.
gpt
The EU is an economic and political union of independent countries.

OK, so what does that actually *mean*?

Firstly, economic union. The EU started out as the EEC (European Economic Community) which was essentially a free-trade pact between some of the major European countries. The idea was that they would reduce and eventually eliminate tariffs and trade regulations between the countries, to make it easier for their companies to sell products and services internationally.

Over time the aims of the EEC widened to include political goals, such as common regulation of laws including those not directly relating to free trade agreements. Notably a treaty in 1992, the Maastricht Treaty, effectively transformed the EEC from a purely trade-based community to become the EU, with a stated goal of "ever-closer economic and political union".

Today the EU comprises 28 countries and over half a billion people. Member states are -- in theory at least -- on a slow but steady progression to ultimately creating a United States of Europe, which would be a federal entity similar in some ways to the USA. 

As part of this there are laws which mean that a citizen of any EU country can go to live and work in any other without requiring any permissions, just as a Californian can go to live in Massachussets without needing a passport or permission to do so. There is also a move towards creating a single currency for all the countries, although not all EU member countries use the Euro, and it looks likely that one of the members, Greece, will soon have to revert to another currency.