Amos 1:15

And their king -The king was commonly, in those nations, the center of their energy. When “he and his princes” were “gone into captivity,” there was no one to make head against the conqueror, and renew revolts. Hence, as a first step in the subdual, the reigning head and those who shared his counsels were removed. Ammon then, savage as it was in act, was no ill-organized horde. On the contrary, barren and waste as all that country now is, it must once have been highly cultivated by a settled and laborious people. The abundance of its ruins attests the industry and habits of the population.