The historian Ibn Khaldun (d. 1405), in his Muqaddimah (Introduction to history), explained historical change and the succession of dynasties as a function of the interactions between nomadic culture and urban civilization. His major contribution is usually considered to be his analysis of the correlation between ‘asabiyya, social cohesion or group feeling, and political power. He argued that the strong group feeling of tribal peoples enabled them to conquer urbanized regions and build regimes and civilizations, but that these conquests were undone by the tribes' gradual loss of ‘asabiyya in the urban setting, leading to new conquests by tribal peoples still strong in desert cohesiveness. Although power was the basis of rulership and royal authority was established through military might, the glue that held societies together was ‘asabiyya, based on kinship and religion and stronger in tribal than in urban society. Conquerors with strong group feeling could create greater and longer-lasting empires because they fielded larger armies and retained their own cultural dynamism for a longer time, and thus were able to defeat their rivals. Conquerors whose social cohesion was weak were soon overcome by the civilization of the conquered and gave way to a new conquering group. Strong group cohesion would also allow royal authority to pass to a second branch of the ruling family if the first was weakened, perpetuating its dominion. The ruler and his army were supported by the wealth of conquest, and returned the people's taxes in the form of gifts and public works. They would be successful only so long as they remained just; as the rulers' level of luxury increased so did their level of exploitation, and injustice soon produced division and “the ruin of civilization.”