A short term violent oppression is more effective in suppressing dissents and opposition. As we have witnessed Mongols brutal campaign that subjugated various and numerous of empires and ethnics. For those who dared to fight them, Mongols killed and genocides all of them. When all the males were killed and females enslaved, there were no opposition except a pile of bones.
For a long term imperialism and colonialism, such occupation would only be effective if integration and forceful assimilation are adopted. Either the rulers adopted the local custom and married the local and integrated into the local or the local subjected to integration by forcing them to adopt the religion, culture, and language of invaders. But either ways, the integration and interracial marriage need to happen. Otherwise, we would have the Western imperialism and colonialism that treated the subjects as slaves or subjects of exploitation which no matter how long and sophisticated would breed resentment and hatred that would be remembered for a long time.
Western imperialism only successes in America as natives were mostly killed, genocide, put into the reserves which is pretty a internment camp or died due to diseases and hunger. Exception is those more populated central American natives that got assimilated through brutal suppression. Canada and the US both have had boarding schools that dragged native children out of reserves and forced them to assimilate or brutally killed for any native kids that didn't behave.
