sentences:  Once a megalithic head-hunting society, its economy was based on agriculture and pig-rearing, and was supplemented by export of captured slaves in inter-village warfare.Although its isolation has contributed to the uniqueness of its culture, the Nias Island chain has been trading with other cultures, other islands, and even mainland Asia since prehistoric time.The predominant religion is Protestant Christianity with over 75% of the population; the remaining are about evenly divided Muslim (mostly immigrants from elsewhere in Indonesia) and Catholic.