The city of Kiev, carrying with it the dignity of the Grand-princedom and the nominal authority over the whole realm, was the key-stone of the body politic as Yaroslav left it, but the loosely-ordered theory of succession which obtained in the Slavonic world led to a perpetual dislocation of this local and ill-defined supremacy, and robbed the arch-throne of any chance of making good its claimed dominion over the other units of the State. Under Isiaslav I. and the brothers, son, and nephew who succeeded him in promiscuous order,[22] Kiev became merely a focussing point for the profusion of quarrels and petty revolutions which were set in perpetual motion by the restless ambition of the neighbouring Princes of Polotzk, Smolensk, and Tchernigov. The last-named province passed into the possession of Oleg Sviatoslavitch[23] (nephew of Isiaslav), and from him sprang the house of Olgovitch, which held the fief of Tchernigov for many generations and convulsed South Russia again and again in its attempts to grasp the throne of Kiev, this hereditary feud of the Olgovitchie with the branch of Vsevolod being the most understandable feature of the prevailing strife-storms of the period. A factor which might have been supposed to make for unity and self-help among the detached Russian rulers, but which instead frequently served to complicate the distresses of the country, was the appearance in the south-east, shortly after the death of Yaroslav, of a new enemy, rising phœnix-like on the ruin of the Petchenigs. The Polovtzi, or Kumans, a nomad race of Turko origin, were even fiercer and more cruel than the tribe they had replaced, and their fighting value was such that the princes, though frequently banding in short-lived leagues against them, were often tempted to invoke their aid in pressing family quarrels, and even stooped to mate with their chieftain women--a woful falling away from the bridal splendours of the Court of Yaroslav.