Final answer:
The causes of World War I were militarism, alliances, imperialism, and nationalism.
Step-by-step explanation:
The causes of World War I can be understood through the acronym MAIN: Militarism, Alliances, Imperialism, and Nationalism. Militarism refers to the build-up of military forces and the belief in the importance of military power. Alliances were formed between countries, leading to a complex network of obligations. Imperialism involved the competition for colonies and resources between European powers. Nationalism, or a strong loyalty and pride in one's own nation, also played a significant role in the buildup to the war.