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I am against regions actually being connected to attackers and defenders. On Testing islands, you don't have to be directly connected to run a TO since coastal regions can be taken over.
Now having a duration is an interesting concept but not sure how practical that would be. I tried it once against Perdan, and it was fun and we fought over 1 region. Since we actually had an end date, despite losing first few battles, Vix still managed to keep their region by pushing hard at the end.
I think destroying a realm is perfectly fine as long as you are not looking to destroy a giant realm. If a realm is left with only their capital + some other non fortified regions, then there isn't much to take from that realm but their capital.
As for White Peace, I wouldn't bother returning regions. It would just end the war right away, leaving the region under the current owners.