I believe it will most likely decrease nationalism across Europe. This is because nationalism depends on the similarities between the people of one country and their differences with the people of other countries. The EU to some differing extent unifies the people of these countries financially, politically, geographically, militarily, etc. The people across Europe will most likely feel more of a citizen of Europe than before when they felt disconnected from other European countries, and often despised these other states as well.
