help with conquering gallic tribes

[os]

theyre all in giant defensive pacts or alliances with like 5+ other tribes, and then i go to war, win, and their capitals cost like 80 for just that one city. is there any way to speed up conquering? i also can only subjugate one nation per war, so it'd take the same amount of wars to integrate.

[Stormy]

There's an option somewhere in diplomatic stance "belicose" that reduces war score cost by 20%

[Iskander]

Do separate peace to annex them one by one. Or wait a few decades, so that they grow larger, then you can conquer several provinces from one war.

[Twelvefield]

Watch out for indomitable villages of Gauls, you can't conquer those, at least not as Rome.

[VladK02]

Do it slowly, one by one. Trick is to take key points in the province you want quickly, an then sue for peace, before allied stacks arrive. Grow bigger by colonization before conquring too. Allies wont help if you are much more powerful then your victim.

But whatever you do, do it in the early game lol because I've got a different problem. The gallic tribes unified on me in the mid-game into a big kingdom, and are rolling into me with 230k armies - many of them. (Im germanic). Thats a bigger problem :)

[Crim]

Did you actually get claims?

When I have claims I can usually take large swathes of territory, but when I just keep doing No CB wars, I can only take 1 or 2 territories