How can I expand my realm without going to war?
Solution 1:
One strategy is to find an unlanded noble who is in line to inherit a title outside your realm, invite them to court, and then grant them a title within your realm that is of equal or higher rank than the one they're set to inherit (i.e. if he's inheriting a county you can't just give him a barony). If the other realm has crown laws set to medium or lower, then the title will fall into your kingdom when they inherit.