I wouldn't consider this "lumping the groups together", or that they must exist together in time... its likely a group may require many generations before they can "oppress" another group.
My list of examples is very similar to this one and the ven diagram here is "was oppressed became oppressor"... in most cases it appears that only if the oppressed are destroyed or I would argue in the case of America- controlled at the margins... then they don't circle back around to abuse their newly acquired power.
My list of examples is very similar to this one and the ven diagram here is "was oppressed became oppressor"... in most cases it appears that only if the oppressed are destroyed or I would argue in the case of America- controlled at the margins... then they don't circle back around to abuse their newly acquired power.