Question regarding best education trait/tree for a 867 tribal custom character.

Got a question, assuming I've got the points for it (or don't care about achievements), what's the best education tait/tree for a 867 tribal custom character? For context this character would be aiming to first elevate the Kingdom of Mann and then eventually establish the North Sea Empire. My instinct says Martial is probably the way to go as I'd need to do a most of this via warfare, but are there arguments for any of the others? Stewardship maybe? Or perhaps Diplomacy? Any advice would be greatly appreciated 🙏🏻