Nonaggression pacts and wars

[Rainshine]

769 Novgorod start. I've expanded out and managed to form Novgorod and have enough land to have Vlad as well. I'm heading for the Slavic Union, but ignoring the distant threats (Francia reaching to Holland, Saxony coming south from Finland) I've got nomads around. So I did what any pagan ruler would do, I married off with the big Khans to get NAPs. For instance, the head Magyar guy's horde is only ~800. One of his clan guys has 6500 though, and I don't want to face that with Light Infantry, so I married off to one of his daughters. Says I have an NAP with him. I declare war on the head Magyar, and the guy who I have an NAP with comes in and wipes out my army. Then I scummed back and quit.
So why is he able to attack me with an NAP, and is there anything else I can do to stop it?

 

[When Horse Archers Attack]

Maybe one of his courtiers fired that event where they ask him to declare war on someone they have a titular claim against, no matter how distant or insignificant the title is in question?

 

[WomboCombo]

Khagans can call in their vassals to wars.

 

[Rainshine]

Tribal lieges can, but I thought that NAPs stopped vassals from being forced into attacking you. Is that Nomad only?

 

[knppel]

Without having tested it, it does make sense to me that a vassal contract overrules such NAP's.
Specially given it was an offensive war of yours, I guess he will casually have called his fellow clans into it.