The assassination of Archduke Francis Ferdinand triggered World War I. But the war had its origins in developments of the 1800's. The chief causes of World War I were (1) the rise of nationalism, (2) a build-up of military might, (3) competition for colonies, and (4) a system of military alliances. The rise of nationalism. Europe avoided major wars in the 100 years before World War I began. Although small wars broke out, they did not involve many countries. But during the 1800's, a force swept across the continent that helped bring abou ....