The first correlation is our first war, when Xibalba managed to raid most of TNN's turf, but couldn't capture a single fort, except for one (back then TNN didn't have access to Fog Warriors + Rain of Stones). Xibalba saw no solution to TNN problem and had to cease fire in order to stop wasting gold and resources on that futile war - there were many other sweeter targets. Like Ulm and Mictlan. Despite being stuck in truly desperate position, TNN refused to cease fire unless Xibalba returns all conquered lands back. Enraged Batman had to agree in the end, but still kept one sweet fort (6 gem income; two provinces away from TNN cap).
After ceasing fire, Xibalba and TNN became rather decent allies for a long time. Xibalba won a war against Machaka; TNN pwnd Arcoscephale. Both of us were growing stroner.
Then came Lizzurd and convinced TNN to jump on Xibalba. It didn't end well for both of them.