Explain why many people call the european union (eu) the “ united states of europe”?

People refer to the European Union as the "United States of Europe" because, like the United States of America, the European Union is made up of individual countries or "states" if you will. Like the United States of America is. 

I don't know this for sure, but here's my thoughts:

The European Union consists of many small nations, some comparable in size to states in the USA. They all work together the the EU and use the same currency, just likes states in the USA. The EU kinda acts like one big nation with little small 'states' inside of them.

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