Having issues with Ireland can I have some advice?

So I got the ball rolling and I can get Desmond. I even (once) was able to get Leinster and Ossory. However at this point I can't get any kind of Casus Beli to continue my conquest for Irish Unity.

I ended up spending my last 20 years of life (playing King Murchad of Munster) doing nothing but waiting for a Casus Beli on Kaldare for the duchy to get Dublin.

Once I died, my son took over and everyone hated me so I ended up with a huge mess, I came out on top after my son and his brother were assassinated and I'm now playing my daughter.

Needless to say I would rather start over and do it right, but I'm not sure what I'm doing wrong. It's not that I don't have the troops, money, prestige or any of that. Just not the darn Casus Beli.