The major causes for World War I. One of the reasons is nationalism. nations want to become the most powerful nation in the world. They will compete for land with other countries, and it usually ends up with a war with the other country. Other countries want to be independent. Militarism was another reason for World War I, was that the army's were rising and becoming stronger by the new technologies like better weapons that can kill multiple people in one shot, also another reason was that the countries started to have allies so some of the con tries would of felt like they were making a plot to take the nation down , so in defense they felt danger and backfired till the cause of the war.