Answer:
Modern Nation Building during the end of the 19th century and early 20th century was perhaps the main contributing factor to the rising tensions in Europe that led to World War I, and World War II.
Step-by-step explanation:
European states used to have a weaker national identity, and in fact, many of them were monarchies that had little power over many of their nominal territories.
With time, however, European states became stronger and stronger, and nationalism was used as a popular feeling to legitimate the nation-state. At the same time, European states began to compete with each other in economic and military power, and these rivalries created so much tension that they led to two world wars.