Archaeologists have often pointed out that culture contact is endemic to human existence. This is a key point, for given its ubiquity; there are many potential forms of interaction and exchange among societies in contact. Culture contacts have involved trade and exchange, warfare, cooperation, competition, and imitation. Colonialism encompasses a large field of study of historical power relations whose legacies are sometimes apparent in the contemporary world. A broad distinction arose between historical and prehistoric archaeologists in some places, resulting in different professional associations, conferences, journals, and even legislation. Kent Lightfoot summarized his concerns 'that the current separation of prehistoric and historical archaeology detracts greatly from the study of long-term culture change, especially in multi-ethnic contexts'. Models to interpret and explain culture contact and cultural change in cross-cultural settings have developed over the last century.