- Nationalism: By the early 20th century, nationalism had become a powerful force in Europe. There was a strong sense of national pride and loyalty, and countries were eager to assert their power and influence in the world.
- Imperialism: Many European countries had empires, and they were often in competition with each other for control of resources and territory. These rivalries played a role in the build-up to World War I.
- Militarism: The major European powers had built up large and powerful militaries. This resulted in a arms race, as countries competed with each other to have the biggest and best armies.
- Alliances: In an effort to protect themselves, many European countries formed alliances with other countries. This created a web of alliances that made it difficult to resolve conflicts peacefully.
- The Assassination of Archduke Franz Ferdinand: The immediate trigger for World War I was the assassination of Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne. His assassination, by a Serbian nationalist, led to a chain of events that eventually led to war.
These are just some of the key reasons why countries entered World War I.