In 622, as we have said, the steppe empire of the Kök Turks stretched from Mongolia to Kyrgyzstan and Kazakhstan, with the valleys of the Orkhon and Chu representing the cores of its eastern and western wings. At both ends the Turks had lively relations with great sedentary empires and civilizations to the south. In the east, China was the immediate neighbor; in the west, Sasanian Iran.

There was one significant diference, however: the buffer zone represented by Transoxania. Its Sogdian princes recognized the suzerainty of the Turkic qaghans ever since their earlier overlords, the Hephtalite kings of Afghanistan, were defeated by a Turko-Persian coalition in the first half of the 560s. Khurasan, also a Hephtalite possession, fell to Iran, and the two empires were thus separated only by the Amu Darya. The sedentary Sogdian inhabitants of Transoxania endeavored to foster peaceful, especially mercantile contacts with all their neighbors, and were content to recognize, as we have said, the suzerainty of the Turkic qaghans. Above all, the Persians made only rare and unsuccessful attempts to penetrate Transoxania, and never the home ground of the Turks in the steppes, in contrast to Chinese diplomacy and military campaigns. A dramatic illustration of the latter is provided by the attacks mounted by the Tang emperor Tai-tsung (600–49; ruled from 627) in 630, and by the reduction, over the next fifty years, of the Kök Turkic empire's eastern wing to the position of a Chinese vassal.