Final answer:
The underlying causes of World War I were nationalism, imperialism, militarism, and alliances. Nationalism led to competition and conflict between European nations, and militarism played a role as well. Alliances further escalated the tensions, obligating countries to go to war when one of their allies was attacked.
Step-by-step explanation:
The underlying causes of World War I were nationalism, opposition to foreign rule, and simmering rivalries between the Great Powers that were exacerbated by treaties requiring allies to enter a war once it began. Nationalism led to competition and conflict between European nations as smaller countries sought their independence from imperial powers. Militarism played a role as well, as countries built up their military capabilities, leading to a focus on arms race. Alliances further escalated the tensions, obligating countries to go to war when one of their allies was attacked.