The First Tevarin War ends in early 2546, as said in the Writer's Guide Part 2, and Ivar Messer rides his following popularity to become a High General. However, it is also said in the Comm-Link 'This Day in History: The Path to Prime Citizen' that Messer is already a High General when the atrocity at Jatta occurs, which is late 2545.
TL;DRThe timeline mistake was acknowledged and hopefully corrected: the war ended early 2546, Messer then became High General, and later became Prime Citizen after the Tribunal was dissolved.
So, full no-prize on this one. After I called it out, I did my research, and there was a mistake in the timelines, which should now hopefully be corrected. So, yes, the First Tevarin War ended early in 2546. After that, Messer went from commander to High General, and as High General he kept petitioning for the dissolution of the Tribunal. While this was going on, all of a sudden there were terrorist attacks associated with the Xi'an that people later claimed were orchestrated by Messer himself, which The Path to Prime Citizen claimed were ongoing, so those happened in summer and fall of 2546. All leading up to when that final big attack occurred, Messer got his way, the Tribunal was dissolved, and he started the position of Prime Citizen, and, oddly enough, in the emergency election on December 15th, 2546, he won. So this should all be reflected now. Thank you very much for catching that. Please, as always, let us know when this stuff comes up.