The divide and conquer stratagem is as old as mankind. There has been enormous efforts over the centuries (religions, Monarchs, Dictators, despots & other rulers of all stripes & colours) to try to convince the gullible masses that the self interest of the small group of ruling elite
does not apply.
The rulers have always been outnumbered, and therefore needed to exert control by manipulating the leaders of various factions into alternatively alliance & war
Machiavelli was the first to really elucidate the art of modern political warfare (with apologies to von Clausewitz, "War is the continuation of politics by other means") in the early 1500's based on the ancient Roman & Greek writings.
If you have 50 minutes, watch this brilliant presentation on Machiavelli & how he codified these ancient strategies into modern ruling techniques.
How Machiavellian was Machiavelli?