The Portuguese maritime expansion from the 15th century led to interactions and trade between Europeans and Africans. In places where the Portuguese established permanent bases, social interaction with Africans entailed processes of biological and cultural mixing, the outcome of which varied significantly depending on the different geographic, demographic, political and linguistic circumstances. In particular historical and social-cultural contexts, acculturation assumed the form of creolisation, a concept that is defined as a process of ethnicisation and indiginisation whereby former ethnic identities disappear and are replaced by a new ethnic identity. According to this definition, Creole societies only emerged in the archipelagos of Cape Verde, São Tomé and Príncipe, but not in the Rivers of Guinea, where creolisation only partly occurred with regard to one particular group. Creole cultures did not emerge in Kongo or Angola either, where local cultures and languages remained largely intact.