The Zhentarim Expedition
Balavasara used to be under the rule of the kingdom as the others were. the only major difference was when the uprising against the True Vryloka occurred the town of Balavasara was hit the hardest as it was were the truth was first discovered and the uprising began. The Vryloka saw to make an example of this so they brought the full force of their warriors down on the uprising town.
They did not realize the extent of the will of the people and their ability to fight them en masse. In result the town burned and thousands died on both sides and the story still reached the ears of the people of the other cities in the region. which then planned a more organized coup that finally brought the kingdom to a fall.