My Romani Campaign somewhere in 230 BC found itself faced against the Averni, Aedui, and Sweboz. Not all of them were allied with each other, but all had declared cease fires. That meant that my beginning expansion into Gaul, Mediolanum and Massilia, were attacked constantly. The only reason why I conquered most of Gaul first, instead of Greece, was because I needed to destroy the Aedui/Arverni/Sweboz unit manufacturing centers.

They kept sending extremely good units, such as Naked Fanatics, that I didnt' have enough cavalry to eliminate. At the same time, I was invested in defending Carthage cause I sent in a naval expedition (which unlike the Romans ones, didn't crash and burn) and took Carthage when it had only 3 defending units. Then took the other 3 provinces around it.

So I was stretched with my main field army in Africa while the barbarians were coming across the borders. It took some years for me to stabilize the situation, but after that it was constant war against Sweboz, Arverni, and Aedui. Whenever I would annihilate (90+% enemy casualties) one of their field armies, the other faction would be right up behind with another nearly full stack.

I never lost any cities but it was quite exciting for awhile, before I broke the backs of the Arverni homeland provinces. After they were knocked out, I could focus on the Sweboz, who controlled Helvetii. Once I gained Helvetti, I could produce much better units such as the Alpine phalanx. But such things took years to build up the necessary infrastructure. All the while, they were attacking emasse, and every province I took to decrease their logistics base, also meant that I was over-extending myself and needed to create more garrison troops.

It was kind of funny how my Romani campaign reversed the Carthage problem so that the Second Punic War never occured, while accelerating Juilius Caesar's Gallic Wars by 2 centuries.