How to get the Irish to expand?

[nzd07]

Once, when I was playing as the english in XL I moved a large army of british north militia out of northumbria to aid my forces in france, leaving a few archers and feudal swordsmen in my castle to keep the scots at bay. To my surprise, it turns out the irish actually bribed my small army and took northumbria. Then, when i took it back, the scots invaded me after realizing how weak my forces were in england. My empire soon collapsed because the scots had built up a huge army. I pulled my king and his army out of brittany to defend mercia from the scots, but then the stupid french overwhelmed me and took all of my french provinces, which led to my quit.

Always remember that the smaller nations can be the ones to screw u over