what ideologies did european countries use to justify their imperialist policies with their own countries and conquered regions?

Imperialism is a policy or ideology of extending a country's rule over foreign nations, often by military force or by gaining political and economic control of other areas.[2] Imperialism has been common throughout recorded history, the earliest examples dating from the mid-third millennium BC. In recent times (since at least the 1870s), it has often been considered morally reprehensible and prohibited by international law. As a result, propagandists operating internationally may use the term to denounce an opponent's foreign policy.