I'm in an interesting Realm Divide situation in my Shimazu campaign. When Realm Divide occurred, I maintained my alliance with Chosukabe and another clan to my south, and I was about three provinces away from Kyoto. Now I have just taken Kyoto, and I have a solid eastern front, but my alliances to the south are beginning to weaken. I figure I probably have three or four turns before my allies to the south become enemies, and I have an entire enemy island to contend with right in the soft underbelly of my realm. Chosukabe seem to be pretty aggressive with naval invasions so far, so it looks like I'll be vulnerable to attack all along the southern coast.