The Philippines consist of a large number of upland ethnic groups living in the country. The highland tribes have co-existed with the lowland Austronesian tribes for thousands of years in the Philippine archipelago. The primary difference is that they were not absorbed by centuries of Spanish and United States colonization of the Philippines, and in the process have retained their customs and traditions. This is mainly due to the rugged inaccessibility of the mountains, which discouraged Spanish and American colonizers from coming into contact with the highlanders.