The first sign that steppe nomads had learned to fight well from horseback was a great raid into Asia Minor launched from Ukraine about 690 bce by a people whom the Greeks called Cimmerians. Some, though perhaps not all, of the raiders were mounted. Not long thereafter, tribes speaking an Iranian language, whom the Greeks called Scythians, conquered the Cimmerians and in turn became lords of Ukraine. According to Herodotus, who is the principal source of information on these events, the Scyths (or at least some of them) claimed to have migrated from the Altai Mountains at the eastern extreme of the Western Steppe. This may well be so, and some modern scholars have even surmised that the barbarian invasions of China that brought the Western Zhou dynasty to an end in 771 bce may have been connected with a Scythian raid from the Altai that had occurred a generation or two before Scythian migration westward to Ukraine.
The Eastern Steppe was, however, too barren and cold for invaders to linger. Consequently, the spread of cavalry skills and of the horse nomads’ way of life to Mongolia took several centuries. We know this from Chinese records clearly showing that cavalry raids from the Mongolian steppe became chronic only in the 4th century bce. China was then divided among warring states, and border principalities had to convert to cavalry tactics in order to mount successful defenses. The first state to do so developed its cavalry force only after 325 bce.
Long before then, however, the Scythians had erected a loose confederacy that spanned all of the Western Steppe. The high king of the tribe heading this confederacy presumably had only limited control over the far reaches of the Western Steppe. But on special occasions the Scythians could assemble large numbers of horsemen for long-distance raids, such as the one that helped to bring the Assyrian empire to an end. After sacking the Assyrian capital of Nineveh in 612 bce, the booty-laden Scyths returned to the Ukrainian steppe, leaving Medes, Babylonians, and Egyptians to dispute the Assyrian heritage. But the threat of renewed raids from the north remained and constituted a standing problem for rulers of the Middle East thereafter.
The Persians, who took over political control of the Middle East in 550 bce, met with little success in punishing steppe incursions. Cyrus the Great, founder of the Persian empire, was killed in 530 bce while leading a punitive expedition against the Massagetai, who lived north and east of the Caspian; and Darius the Great met with indifferent success in 512 bce when he tried to subdue the Scyths from Europe by crossing the Danube. On the other hand, diplomatic arrangements whereby border tribesmen were paid to guard against raids from deeper in the steppe worked well as long as Persian tax collectors provided a suitable assortment of goods with which to subsidize the friendly borderers. No massive incursions or large-scale infiltrations from the steppe into the Middle East took place, therefore, until after the overthrow of the Persian empire at the hands of Alexander the Great in 330 bce.
In the next century, however, the collapse of the Persian frontier guard in Central Asia and the consolidation of a new steppe empire based in Mongolia combined to provoke large-scale displacements of peoples westward along the steppe and southward from the steppe onto cultivated ground. For the first time, the natural gradient of the Eurasian Steppe came fully into play when a tribal confederation, called Xiongnu by the Chinese, attained an unmatched formidability. This happened at the very end of the 3rd century bce. Neighbours on the steppe, fleeing from the Xiongnu, moved south and west, generating in turn a wave of migration that eventually reached from the borders of China as far as northwestern India and the Roman limes along the Danube.
The Xiongnu empire
Just as the Scythian empire of the Western Steppe was a mirror image of the Persian empire to the south, the empire of the Xiongnu (late 3rd century bce–2nd century ce) mirrored the Chinese empire that had been consolidated in 221 bce by Qin Shi Huang Ti and was subsequently stabilized under the Han dynasty (206 bce–221ce). To judge from Chinese accounts, which are the only ones available, the Xiongnu modelled themselves quite closely on Chinese principles, regarding their ruler as the Son of Heaven, just as the Chinese did. Organized warfare across the Gobi alternated with periods of peace, when formalized exchanges of tribute-gifts allowed the rulers on each side to strengthen themselves by acquiring rare and valuable goods to distribute as they saw fit. The Chinese obtained horses for the army and other Imperial uses, while the Xiongnu ruler acquired grain, silks, and other luxuries with which to reward his followers.