Final answer:
Nationalism was a significant movement that created tension in Europe during the early 1900s, leading to conflicts such as World War I.
Step-by-step explanation:
During the early 1900s, nationalism was one of the movements that created tension in Europe. Nationalism, a belief in the superiority and interests of one’s nation, often played a role in the polarization of European countries and fueled an arms race, leading to entangling alliances and ultimately conflicts such as World War I.
This tension was part of a broader European power struggle including imperialism and competition over colonies, which also contributed to international conflicts.