As the title describes, I was at turn 117 as Morgur appeared for the second time. At this point, I had a stable military alliance with Durthu, who had ~14 provinces. Favor was at 80, with no negatives. Morghur shows up, does his waterfall intro, and then boom - I'm at -10 amber because my military alliance with Durthu broke for no good reason.
I'm now completely stuck because I'm at -10 amber, cannot re-initiate a military alliance with Durthu (I've tried), and I can't wage war against him without replenishment. At turn 117, this really sucks. If there was any reason for the alliance breaking, or any indication that it would, I'd be able to avoid this situation.
I believe this is a bug, since it doesn't seem at all logical.