Five hundred years later the Hyborian civilization was swept away. Its fall was unique in that it was not brought about by internal decay, but by the growing power of the barbarian nations and the Hyrkanians. The Hyborian peoples were overthrown while their vigorous culture was in its prime. Yet it was Aquilonia's greed which brought about that overthrow, though indirectly. Wishing to extend their empire, her kings made war on their neighbors. Zingara, Argos and Ophir were annexed outright, with the western cities of Shem, which had, with their more eastern kindred, recently thrown off the yoke of Koth. Koth itself, with Corinthia and the eastern Shemitish tribes, was forced to pay Aquilonia tribute and lend aid in wars. An ancient feud had existed between Aquilonia and Hyperborea, and the latter now marched to meet the armies of her western rival. The plains of the Border Kingdom were the scene of a great and savage battle, in which the northern hosts were utterly defeated, and retreated into their snowy fastnesses, whither the victorious Aquilonians did not pursue them. Nemedia, which had successfully resisted the western kingdom for centuries, now drew Brythunia and Zamora, and secretly, Koth, into an alliance which bade fair to crush the rising empire. But before their armies could join battle, a new enemy appeared in the east, as the Hyrkanians made their first real thrust at the western world. Reinforced by adventurers from east of Vilayet, the riders of Turan swept over Zamora, devastated eastern Corinthia, and were met on the plains of Brythunia by the Aquilonians who defeated them and hurled them flying eastward. But the back of the alliance was broken, and Nemedia took the defensive in future wars, aided occasionally by Brythunia and Hyperborea, and, secretly, as usual, by Koth. This defeat of the Hyrkanians showed the nations the real power of the western kingdom, whose splendid armies were augmented by mercenaries, many of them recruited among the alien Zingarans, and the barbaric Picts and Shemites. Zamora was reconquered from the Hyrkanians, but the people discovered that they had merely exchanged an eastern master for a western master. Aquilonian soldiers were quartered there, not only to protect the ravaged country, but also to keep the people in subjection. The Hyrkanians were not convinced; three more invasions burst upon the Zamorian borders, and the Lands of Shem, and were hurled back by the Aquilonians, though the Turanian armies grew larger as hordes of steel-clad riders rode out of the east, skirting the southern extremity of the inland sea.