Philippine society was relatively homogeneous in 1990, especially considering its distribution over some 1,000 inhabited islands. Muslims and upland tribal peoples were obvious exceptions, but approximately 90 percent of the society remained united by a common cultural and religious background. Among the lowland Christian Filipinos, language was the main point of internal differentiation, but the majority interacted and intermarried regularly across linguistic lines. Because of political centralization, urbanization, and extensive internal migration, linguistic barriers were eroding, and government emphasis on Pilipino and English (at the expense of local [languages]) also reduced these divisions. Nevertheless, national integration remained incomplete.
Through centuries of intermarriage, Filipinos had become a unique blend of Malay, Chinese, Spanish, Negrito, and American. Among the earliest inhabitants were Negritos, followed by Malays, who deserve most of the credit for developing lowland Philippine agricultural life as it is known in the modern period . As the Malays spread throughout the archipelago, two things happened. First, they absorbed, through intermarriage, most of the Negrito population, although a minority of Negritos remained distinct by retreating to the mountains. Second, they dispersed into separate groups, some of which became relatively isolated in pockets on Mindanao, northern Luzon, and some of the other large islands. Comparative linguistic analysis suggests that most groups may once have spoken a form of "proto-Manobo," but that each group developed a distinct vernacular that can be traced to its contact over the centuries with certain groups and its isolation from others.
With the advent of Islam in the southern Philippines during the fifteenth century, separate sultanates developed on Mindanao and in the Sulu Archipelago. By the middle of the sixteenth century, Islamic influence had spread as far north as Manila Bay.
Spain colonized the Philippines in the sixteenth century and succeeded in providing the necessary environment for the development of a Philippine national identity; however, Spain never completely vitiated Muslim autonomy on Mindanao and in the Sulu Archipelago, where the separate Muslim sultanates of Sulu, Maguindanao, and Maranao remained impervious to Christian conversion. Likewise, the Spanish never succeeded in converting upland tribal groups, particularly on Luzon and Mindanao. The Spanish influence was strongest among lowland groups and emanated from Manila. Even among these lowland peoples, however, linguistic differences continued to outweigh unifying factors until a nationalist movement emerged to question Spanish rule in the nineteenth century.
Philippine national identity emerged as a blend of diverse ethnic and linguistic groups, when lowland Christians, called indios by the Spaniards, began referring to themselves as "Filipinos," excluding Muslims, upland tribal groups, and ethnic Chinese who had not been assimilated by intermarriage and did not fit the category. In the very process of defining a national identity, the majority was also drawing attention to a basic societal cleavage among the groups. In revolting against Spanish rule and, later, fighting United States troops, the indigenous people became increasingly conscious of a national unity transcending local and regional identities. A public school system that brought at least elementary-level education to all but the most remote barrios and sitios (small clusters of homes) during the early twentieth century also served to dilute religious, ethnic, and linguistic or regional differences, as did improvements in transportation and communication systems and the spread of English as a lingua franca The First Phase of United States Rule, 1898-1935 , ch. 1) -->.