Back in the days of the old Fanaticus DBA Resource page (yes, I've been away that long) there were rules for a Conqueror campaign. The basic gist was an army that had kicked butt in reality would take on one opponent after another, trying to beat all of them.
One player would take the conquering army and see how far they could get. In 1/72 plastic, our Polybian Romans would first take on the Carthaginians, who rarely won. Next up was the Gallic army, which had a decent record against the Romans. Then our Mongols stood in for Parthians and the Roman invaders usually had a long, hard day.
After everyone who wanted had a crack at it, we'd see who had the best record as conqueror and who was the toughest opponent. We tried this with the Mongols, using the Sung as the first opponent - wrongly, since really it should be the Jurchen Chin. Next up were the Rus and last the Teutonic Knights but the Conquest Mongols never got past the Sung and their massed crossbows, not that we played this often. Then we drifted into black powder rules and let DBA lie fallow for years.
Anyway, other choices of conquerors/victims could be Alexander/Greeks/Persians/Indians, or Caesar/Gauls/Macedonians/Parthians, etc.
I guess tie breakers could be like the world cup, with elements lost against elements wiped out.
Or perhaps the Conquest campaign rules are stashed somewhere that I have not figured out yet.
Poking around old files on my hard drive, I found an account of the Rome Conquest campaign our crew played back in 2013. It gave us a good 3 sessions of fun minus the angst of "gang up on the leader" found in many other campaigns. But while the account of the campaign brought back fond memories, it became obvious I'd not written down the coring system. Oh well, perhaps I'll just crib World Cup scoring for the next time we get around to this.
We had 4 players each take the Polybian Romans and take on first Carthage, then the Gallic army and last the Parthians (the Mongols stood in for them), all in 1/72 plastic. If the Romans lost any battle their conquest ended. Carthage lost all 4 games. The Gauls won twice and lost twice. The Parthians won both times. Rick and I tied for First Man in Rome with 12 points each. The tie breaker was supposed to be a Roman civil war battle, but Rick was not able to attend the next meeting so it was settled with a die roll and he won. Our late member Tom was the first enemy of Rome by far with 17 points, having derailed a number of marches to triumph. As far as I can tell we gave 2 points for a win and 1 point for each enemy element or equivalent dispatched. This allowed points for losing armies that caused a lot of damage on their way down. But some of the scores don't quite jive with this. Not sure if I just made mistakes back then or the rules had some other quirk.