Final answer:
The primary cause of World War I was a combination of nationalism, imperialism, and militarism.
Step-by-step explanation:
The primary cause of World War I was a combination of nationalism, imperialism, and militarism. Nationalism, which is a strong loyalty and pride towards one's own nation, was a driving force in the conflict as different nations sought to assert their dominance and protect their interests.
Imperialism, the policy of extending a nation's power and influence through colonization and territorial acquisition, also played a role as European powers competed for resources and territory around the world. Militarism, the belief in the importance of a strong military and readiness for war, further escalated tensions between nations.