Rising nationalism in Europe runs counter to the mission of the European Union. Nationalists support their own country's interests, even if they harm outsiders. An organization like the European Union supports the common good of all above the interests of any one nation. The conflict inherent in this equation has lead to movements like Brexit.
ISIS, Al-Qaeda, and other Islamist groups have carried out numerous terror attacks in Europe in the last few years. The deadliest attack was the November 2015 Paris attack in which 130 people were killed, but others have occurred in England, Spain, Belgium, Germany and other places. Many of the attacks occur in symbolic locations and seek to undermine Western authority.