Answer:
Nationalism has been an important trend in European political landscape all the way from the Spring of Nations that have started 1848. In the first half of the 20th century it took acute radical with pinnacle of the Nazi Germany atrocities.
The European Union project was formed with the goal of cooperation between countries and prevention of war between them. Meanwhile, due to the fear that European Union will lead to the loss of the sense of national identity, multiple right-wing parties occupied strong positions in many EU member states with a visible rise in the beginning of the 21st century. This trend reached its highest point due to the Migration Crisis that started in 2015. The biggest example is Hungary were far-right conservative parties Fidesz and Jobbik enjoy the major support in the country.