I'm playing Friesland, and I've made Munster a march. I can set Munster as my rival, and even directly DoW it (without first revoking march or vassal status). That... seems a little strange, no?
I did a little more experimentation —*rivaling your march does make relations terrible, but won't break the march relationship, and they'll still happily join in your wars. If you declare war on your march, this does (permanently) break the march relationship, but otherwise has no ill effect (no stability drop, e.g.).
I did a little more experimentation —*rivaling your march does make relations terrible, but won't break the march relationship, and they'll still happily join in your wars. If you declare war on your march, this does (permanently) break the march relationship, but otherwise has no ill effect (no stability drop, e.g.).