Final answer:
The least significant long-term cause of World War I was the rise of nativism.
Step-by-step explanation:
The least significant long-term cause of World War I was The rise of nativism.
The main causes of World War I were militarism, alliances, imperialism, and nationalism. However, while the other options - the formations of secret alliances, the spread of imperialism, and increased militarism - played significant roles in the buildup to the war, the rise of nativism had a lesser impact.
Nativism refers to a preference for native-born inhabitants over immigrants. While there were instances of nativism in certain countries during this period, it did not have the same far-reaching and interconnected consequences as the other causes, which contributed to tensions and rivalries among nations.