Christians were persecuted by the Roman Empire, then became conquerors of the world.
Russians were oppressed by the Mongols, then became conquerors of Eurasia.
Communists were oppressed by Tsarists, then became ruthless oppressors themselves.
Protestants were oppressed in Europe, so they set sail to America and became oppressors of the natives.
Just think of any powerful nation (or group of people, or whatever), and try to think of somebody they have oppressed, or are still oppressing. It's typically not hard to come up with examples.
The better explanation is simple and banal - power concentration makes people abuse it.
Neanderthals aren’t going to become oppressors.
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.
You don't need to go that far forward, though. It took Christians <400 years to promulgate the Edict of Thessalonica that made Christianity (and of a very particular kind at that!) to be the only legal religion. And one can argue that it's no coincidence that it happened pretty much as soon as they have gained the political upper hand in the Roman Empire.
> Same for Russians and Mongols, there's a pretty large gap with a ton of events in between
Not really. Muscovy was still paying tribute to the Golden Horde and recognizing their supreme authority under Ivan III. His grandson Ivan IV ("the Terrible") conquered the Tatar state, making its lands such as Kazan part of his empire, and sent an expedition to start the conquest of Siberia.
The inaccuracies here are not so much with timing, more so with lack of precision wrt the groups involved. In general, though, I think it's fair to say that, for most part of human history, the oppressed become the oppressors pretty much as soon as they are capable of it.
>In general, though, I think it's fair to say that, for most part of human history, the oppressed become the oppressors pretty much as soon as they are capable of it.
Doesn't this also hold for non-oppressed that have the opportunity? Although I suppose it'd be hard to find any examples of non-oppressed groups. Pillaging or conquering neighbors was pretty much the norm throughout the history. Rus' was converted to Christianity in part to stop raids such as Siege of Constantinople of 860.