I think Roman Rebels could be a different sub faction though. Maybe they would pop up when cities have low public order or something. I will stick to the Latins.
Now I will finish up the minor players in Italy:
Etruscans
Sub-faction to: Rebels
Settlements: Arretium
Unique Troops: Etruscan Hoplites (?)
Significance: Were barely hanging around at this point, and were located around Arretium. The Romans conquered Arretium in the late 4th centurey BC. The Etruscans were involved in the Third Samnite War which ended in 290 BC, and the Romans campaigned against them in the years after that. I believe the Etruscans were fully subdued sometime in the 260's BC. So my thought would be for maybe some scripted armies to appear now and then until a certain time period or maybe until a certain building is built in Arretium.
Alternate Campaign: No
Umbrians
Sub-faction to: Rebels
Settlement(s): Ariminum
Unique Troops: Umbrian Hillmen (?)
Significance: Really they would pretty much be exactly as the Etruscans. Right now Ariminum is not a city. Instead it is Caesena. I don't know if Rome owned this city or not in 280.. My sources say Rome didn't take Ariminum until 268 BC. So we will have to see.
Alternate Campaign: No
Piceni
Sub-faction to: Rebels
Settlement(s): Ancona
Unique Troops: Piceni Spearmen (?)
Significance: Not much is really known about them, except that they lived on the east coast of Italy where Ancona is. Would probably not appear much.
Alternate Campaign: No
Campanians
Sub-faction to: Rebels
Settlement(s): Capua
Unique Troops: Campanian Hoplites (?) Campanian Cavalry (?)
Significance: I believe they were fully subdued by the Romans at this time as Capua was one of Rome's most important allied cities. Nonetheless they offer good AOR troops.
Alternate Campaign: No
Samnites
Sub-faction to: Rebels
Settlement(s): Malventum
Unique Troops: Samnite Spearmen, Samnite Swordsmen (?)
Significance: Were finally subdued in 290 BC, but it's only ten years after that. I believe they could still be hostile, and maybe pop up if Pyrrhus is successful. They were major players in the Social War.
Alternate Campaign: No
*Lucanians, Bruttians, Messapians, Marsi
Sub-faction to: Rebels
Settlements: Varies. Essentially none, but the Lucanians could have Tarentum, Messapians Croton, and Bruttians Rhegium if given the oppurtunity maybe? Reason that I am not sure is the fact that Tarentum would be the Tarentines, and Croton and Rhegium as their own city states.
Unique Troops: Lucanian Skirmishers (?) Bruttian Infantry (?) Marsian Spearmen (?)
Significance: They might not even make it as sub-factions, hence the asterix. The only way these peoples would get represented is by their units. However I have an idea that even though Tarentum would be owned by the Greeks, that a Lucanian army could still pop up in the area? Or the Marsians could pop up randomly throughout Italy?
Alternate Campaign: No
Ligurians
Sub-faction to: Rebels
Settlement(s): Genua
Unique Troops: Ligurian Infantry (?) Ligurian Cavalry (?) Ligurian Skirmshers (?)
Significance: The Ligurians were their own people, many ancient scholars place them around Massilia and even as far as Iberia. However they were located around Genua (their main city). They were used a lot as mercenaries for Carthage and Greek city states. They were finally subdued by the Romans in the 2nd century BC
Alternate Campaign: No
Veneti
Sub-faction to: Rebels
Settlement(s): Patavium
Unique Troops: Veneti Hoplites (?) Veneti Skirmishers
Significance: Were around until at least the 2nd Punic War where they allied with Rome and sent troops to Rome to aid them when Hannibal was campaigning. In 302 BC they were attacked by a Spartan Naval force but they captured and destroyed their ships. They warred with Celtic peoples in the area and allied with the Cenomani. The Veneti are debated to be Illyrian but they could also be Italian, or even a mix.
Alternate Campaign: No
Croton
Sub-faction to: Rebels
Settlement(s): Croton
Unique Troops: None
Significance: A greek city state, I believe Rome had occupied Croton a little before 280 BC due to Lucanian and Bruttian Raids. Also I believe this occupation sparked the conflict with Tarentum. Crotn defected to Hannibal and served as his base of operations during the 2nd Punic War.
Alternate Campaign: No
Mamertines at Rhegium
Sub-faction to: Rebels
Settlement(s): Rhegium
Unique Troops: Mamertine Infantry (?)
Significance: Another greek city state, it's Roman garrison defected to the Mamertines in 280 BC as the garrison consisted of mainly Campanian troops of similar stock to the Mamertines. Held off Bruttian raids, and Pyrrhus. Was captured by the Romans in the late 270's BC and the traitors were taken to Rome for trial and execution.
Alternate Campaign: No
Okay so there are all of the minor sub-factions that could possibly be encountered in the campaign. Notice how I put a '(?)' after most of the troops. That is because I still need to figure out what I want to do for units in the Italian AOR. I could do what RTR Platinum and just make 'Italian Troops' or I could go with the proposed units above.
Now onto the three Major sub-factions, that will be playable through alternate campaigns:
Insubres
Sub-faction to: Rebels, Gauls
Settlement(s): Medilanium, Accerae
Unique Troops: Insubres Infantry (?) Insubres Cavalry (?)
Significance: The Insubres will represent the Cisalpine Gauls who were not finally subdued until after the second Punic War.
Alternate Campaign: Yes, through the Gauls faction
Goals: Hold Northern Italian Provinces, defeat Romans
Boii
Sub-faction to: Rebels, Gauls
Settlements: Bononia, a settlement yet to be determined north of Pannonia
Unique Troops: Boii Infantry (?)
Significance: The Boii were an interesting faction who were split. Half being in nothern Italy and half being in south-eastern germany. They will be fun to play as in my mind. Right now Felsina is Bononia.
Alternate Campaign: Yes, through the Gauls faction
Goals: Hold Northern Italian and Pannonian Provinces, defeat Illyrians
Tarentum
Sub-faction to Rebels, Greeks
Settlements: Tarentum
Unique Troops: Tarentine Leukaspides (?), Tarentine Cavalry (?)
Significance: The strongest city state in Italy, the Tarentines began a War with Rome that drew Pyrrhus into Italy. They will be allied to Epirus and should aid in the fight with Rome. If successful they could turn on Epirus, take Rome, or venture to Sicily. It will be a tough campaign but worth the challenge.
Alternate Campaign: Yes, through the Greek faction
Goals: Take southern Italian Provinces, Syracuse, defeat faction Rome
So all of Italy is now represented, if anyone has any more suggestions for Italian peoples let them be known. However if you do, please use cities from the city list in the OP. I will move on to Sicily and Sardinia/Corsica later.