Txolla, on the other hand, is indefensible and has already been attacked, repeatedly, every few years.
Txolla is only indefensible without Black Sheep. If we can secure that, we're fine. The western border of Txolla actually belongs to the Highland Kingdom who've been dedicatedly forting up their little slice of paradise since the Godfist Incident. There's no way for them to be easily dislodged.
The area between us and Khemetri is the Arabian Peninsula which is mostly desert. It's not easy to move an army through there since you're utterly dependent on oasis and water resources. It would be relatively easy to fortify it and make it virtually impregnable.
E:
Is Greenshore flat enough for Heaven's Hawks to have an advantage?
I would think so. Stymyr looks like it holds most of modern-day Romania. The westernmost part in Transylvania would be hilly and mountainous, but the rest is a flat river valley.
With the new information Behryvar-Tarta relations, I am still inclined to continue to try and sell guns to Behryvar. An unlikely loss of opinion is worth the money, especially since it seems like Tarta dislikes Styrmyr enough for us to work together against them even if they aren't particularly fond of us.
I'm wondering, depending on how the war goes, do we want to think about annexing Stymyr? They're of the People, even if of a misguided type. The fact we allowed a group of People to leave during PoC and become slaving barbarians has never sat right with me.
Greenshore's borders are not defensible unless we push them back to the Carpathian mountains and that appears to be most of Stymyr's land. Securing the border will mean a lot if we're ever confronted by hostiles elsewhere or the Ymaryn weaken. Tarta may be willing to help in exchange for monetary concessions or land that they claim as theirs but was taken by Stymyr in the past.
If it comes to war, we're going to probably need to throw a City Levy at Stymyr either way and if we're investing that much, we may as well go for gold. If they're anything like us, taking an inch or taking a mile of their land doesn't matter, they won't tolerate either.
OTOH Sacred Warding requires enough input from us that it can't spread on its own like anti-cholera so we don't have to concentrate the gifts into as few turns as possible.
The other thing is: Cholera was endemic to eastern India and was one of the deadliest diseases on the sub-continent. Even today, bad water and diarrhea are one of the leading causes of death in rural India (~50% of the population are at risk). Cholera never expanded beyond India until colonialism in the 1800s. The fact the Cholera is a problem at all is ahistorical and something AN acknowledged was a mistake. The Saffryn Sea powers likely care about the cure for Cholera a lot less than Kus where the disease is absolutely endemic. Rehydration therapy will be helpful for Saffryn Sea powers, but it is nowhere near as game changing as it was in Kus where it saves thousands of lives each year.