The European Union

What is the EU?
How did it develop? 
What are the current challenges facing the EU?
Why did Britian vote to leave the EU?
Think about in other words the role of conflict, The EU and United States, Concept of shared currency, Comparisons within the EU, Problems of economic nd political union. 
-Must be 800 words
-Least 4-5 citied sources from a reliable source such as books or a university website.