Yelithan-Kamithreyan war
3rd war

Kamithreyans were like "we need to use some of your land because we don't have enough" and Yelithans were like "we barely have enough" and they couldn't expand in other directions for geographical reasons, and things escalated over time until it was a war!
It really didn't have to be one, but there were some miscommunications and high tensions involved.