Historical and ethnic studies published and promoted by the various ruling classes during their governance over Malta provide little, if any, valuable guidance on the question of Maltese ethnicity, given that their conclusions appear to have been driven, in large part, by political expediency. Hence, Maltese history books published during the rule of the Knights of St. John, at a time when Malta and Gozo suffered repeated "razzias" at the hands of the Ottomans and Barbary corsairs, promoted the myth of a continuous, Roman Catholic, native Maltese population, that somehow survived despite the Arab conquest of Malta and the depopulation that followed. Studies and reports published during the British colonial period promoted the theory of Phoenician origins, in an attempt to distinguish the Maltese from their Sicilian and Italian neighbours, or in the case of the Catholic Church, to distinguish the Maltese from the Arab peoples that controlled Malta prior to the liberation of Malta by the Normans. By contrast, history books published during the Mintoff years following Independence began to question the earlier beliefs in a continuous, indigenous population of Christian Maltese and, in some cases, quietly promoted the theory of closer cultural and ethnic ties with North Africa. This new development was noted by Boissevain in 1991: