What negative drawbacks did nationalism and imperialism in european countries create?

Nationalism has been the object of numerous criticisms throughout history. In Europe this ideology broke with the social coexistence that the different cultures and nationalities had, spreading a feeling of natural superiority of one ethnic group over others.

Imperialism, propitiated the beginning of an increase in the military power of the European powers, as they fought each other to get more power over the different colonies.

Both sentiments, nationalism and imperialism, were factors that led to the Second World War, took European countries to their limits and produced innumerable losses in all areas of their lives.

c it says nothing about connecting those 2 seas.