In my only really long campaign in this game, as Epeiros the romans were my allies for 40 years and did nothing, nada, zip. They didn't even try to capture the rebel provinces to the north. Then about 40 years in, they just took three stacks north and took Bonnonia and Segesta and were marching on Mediolanum (I had Patavium though), when they blockaded a port of mine, causing a war. Idiots. It's like some stupid nauarch just decided to attack a random port and caused a big war. Well it was big because I wiped them off the map within about three years after they triggered a war. But at least they had started getting active finally.