It is good to trust in your vassal?

[GaborMania]

I play as Hre and I wanna send 3 full armies in poland to reinforce that region.France is my vassal but they have a very good army and they are the richest.Should I trust them and send my armies to poland and leaving the western front undefeated?

[Vampiresbane]

I'm fairly sure vassals cannot attack their protector. Now if you attack an ally of your vassal, your vassal will break his alliance with you and then he acts like a normal faction and then can attack, but as a vassal he'll mainly just defend himself.

[Hmm Perhaps]

Hold one army back just in case, but as a vassal the AI tends to not attack unless neighbouring regions are very poorly defended.