What was one of the challenges facing the european union in the early twenty-first century

During the early 21st Century the European Union expanded to include numerous eastern European countries of Poland, Lithuania, Hungary etc.

While, this gave the EU larger economic and political power, it also created problems.

The countries in Eastern Europe were on a totally different level of socioeconomic development.

After a few years, the rifts became even more clear with the economic recession, the problem of migrants and the rising right wing political movements in EU countries.

Today, there is a problem of nationalism, which is a threat to the EU, which otherwise works to look beyond nationalism and promotes collectivism.

Correct answer for apex is d.