Rome 2 DEI: how do you get some faction campaigns off the ground?

Specifically I’m playing Roxolani. I start with 1 settlement that doesn’t make a lot of money, I can build an army and upgrade my buildings with the starting money but by the time I have an army the next nearest faction has 2 and I can’t defeat 2 armies plus the garrison. I really can’t even defeat 2 armies, and I definitely can’t afford to create a second army. Is there something I’m missing?