I't be nice to see the Illyrians (essentially, they are what yiu get when you put pre hellenized -before Greek influnces- Romans in the Balkin peninisula; exceptional fighters (and reamained so for mostr opf Roman history, becoming int he 3rd century, the main peoples from which legionaries were recruited from, taking Italy's place), famous pirates, and were well on thier way to becomming an established power when Rome began a peice meal conquest of the area.
-on another note, it was also the Illyrian rebellion that stopped Rome from conqeroing Germany- many will say its the ambush in teotoburg forest, but in reality, all the germans did was stick thier arse in a hornets nest with that one, and the Romans quicklly launched a massive expedition solelly meant to ruin the countrey side and teach the germans a lesson they would never forget (and promptlly afterward, thier was the Pax Romana

)- but, one may ask, if the Romans could so easilyl launch a campighn of destruction, why not another one of Conquest?
The answer is that the single most serious revolt in all Roman history was occuring in the Illyrian provinces- why was it so serious? Because for the only time in Roman history, several Legions joined the people in thier rebellion, creating a dire situation in which monumanetal forces needed to be dispatched- forces that could have been used to occupy Germany in a second invasion, as its one thing to go through, burn everything you see, and then head back- another thing to go in, and actually set your arse down, and begin to say its yours, and the second requires a great deal more troops to do then the first.