Hm. You're sure that they hadn't had some diplomat down there softening things up? Because those "strongly object" messages should only happen when a region is highly sympathetic/loyal to the realm in question. Like,
No, it means that you can't just have 1 realm declare war on 1 other realm; you need a large coalition before it even becomes a worry.
Why would our regions have high sympathy and loyalty to Sanguis Astroism, who are thousands of in game miles away from Aurvandil and have had no interaction with us?
And yes, that is my point, when you get a large coalition you find yourself with the power to immediately win by collapsing your opponent internally just by declaring war, which largely make Sanguis Astroism all the more untouchable.
