Which of the following is considered a current challenge facing Europe in the 21st century?

Political extremism and migration crises are significant challenges facing Europe in the 21st century due to various factors, including the influx of refugees from conflict zones, economic migrants seeking better opportunities, and the rise of nationalist movements that often react negatively to these demographics. The migration crises have put pressure on social services, led to tensions within and between nations, and fueled debates over cultural identity and national sovereignty. This situation has been further complicated by the economic disparities among EU nations, which can influence the political climate and societal cohesion.

In contrast, the other options do not accurately capture the pressing issues currently affecting Europe. Economic prosperity is uneven, but it is not a uniform challenge; rather, it is a reflection of underlying disparities. Increased national isolationism does exist but is more a symptom of the larger issues of political extremism and societal division rather than a standalone challenge. Lastly, while technology continues to evolve significantly, it is not widely considered to be in decline; rather, Europe faces challenges in keeping pace with global technological advancements, but this is not a crisis by definition.