there was an economic and social crisis in the community in the 16th century, attributable to over-population and environmental deterioration. This resulted in the population being divided into two separate groups of clans who were constantly involved in warfare. The warrior class that evolved from this situation gave rise to the so-called Birdman cult, based on the small islands offshore of Orongo, which superseded the statue-building religion and threw down most and slighted most of the moai and ahu.