The United States gained authority over the Philippine Islands as a result of the Spanish-American War (1898) and the Treaty of Paris (1899), which recognized American wartime territorial gains. Prior to that time the Spanish had general authority over the northern region of the Islands down to the Visayas, which they had ruled from their capital at Manila on Luzon for nearly three hundred years. The population in that Spanish zone was Christianized as a product of deliberate Spanish policy during that time frame. The area to the south, encompassing much of the island of Mindanao and all of the Sulu Archipelago, was under Spanish military control at the time of the Spanish American War (1898), having been taken over in the previous fifteen years by a protracted military campaign. This southern territory was held by the presence of Spanish military units in a series of strong forts located throughout the settled areas, but clear control over the society was quite weak and, in fact, collapsed after the American naval victory at Manila Bay. The United States did not establish its own presence in much of the southern region until 1902. It based its claim over the region on the treaty with the Spanish, and other colonial powers recognized that claim as legitimate.