The Euro is the currency in many EU states. This was hard to imagine in the past. Crossing borders without stopping at check points also used to be impossible. Studying in another country without difficulty was also considered impossible. Yet all of these things are now possible. That is why many people say the EU is a success. They say: the countries should work together more often.
Other people disagree. They say the EU has too much power. They say individual states should be able to make their own decisions. They say the rights of individual states are threatened.
Some people want more EU influence, others want less EU influence. There are often arguments about this in the European Union. The United Kingdom even had a referendum in 2016. A small majority said: it is better for our country to leave the EU.