2. Militarism: European countries built up their militaries in response to each other's perceived threats, leading to an arms race.
3. Alliances: European countries formed alliances with each other in an attempt to protect themselves and gain an advantage in the event of war.
4. Nationalism: A sense of national pride and identity grew in European countries, which led to competition and rivalry between them.
5. The Assassination of Archduke Franz Ferdinand: The heir to the Austro-Hungarian throne was assassinated by a Serbian nationalist in 1914, which triggered a series of events leading to war.
6. The Breakdown of Diplomacy: Diplomatic efforts failed to resolve tensions between the European powers, leading to the outbreak of war.