The absence of centralized power meant that a small number of Spaniards were able to convert a large number of Filipinos living in politically autonomous units more easily than they could have, say, converted people living in large, organized, complex kingdoms such as those Hinduized or (later) Theravada Buddhist-influenced kingdoms in mainland Southeast Asia and on the island of Java in Indonesia. The Spanish were unsuccessful in converting Muslim Sultanates to Christianity, and in fact warred with Muslim Filipinos throughout their 300 year colonial rule from 1521 - 1898. Nor did they successfully conquer certain highland areas, such the Luzon highlands, where a diverse array of ethno-linguistic groups used their remote, difficult mountainous terrain to successfully avoid colonization