After World War II European nations created a number of free trade agreements amongst themselves. While today some will claim that the EU was created to prevent more European wars, that was not was discussed at the time. The treaties were created so that they could rebuild their steel and coal industries. Later these free trade agreements became treaties which began to have a greater reach into the sovereignty of European countries. Eventually a political and economic union was created. The political union is known as the European Union or EU for short. The economic union is known as the Eurozone; but, England did not adopt the Euro and kept it's currency known as the pound.
Now the people in those European countries do not get to vote for the people who write the laws for the European nations. The people who vote on the laws are appointed by their countries leaders. The bigger problem is that the people of the European Union didn't vote for that either. Well, currently the EU writes 70% of all the laws that Britain must follow and not all of the people in England are happy with this so they want to vote to see if Britain should leave the EU, that vote is called the Brexit. In three paragraphs you now know more about the EU than about 90% of all Americans. Their vote will happen in the next couple of months. Understand what happens there and you will understand what is happening here and why democracy, nationalism and populism matter.
YouTube - #Brexit: A Reason to Care.