The vast belt of open grassland running almost unbroken across the middle of Eurasia, from the plains of Hungary to the borders of China — too dry across much of its belt for reliable farming, but ideal for pasture and the horse, which for some three thousand years turned the peoples who lived on it into the most mobile warriors on earth and made the steppe at once the great engine of nomad empire and a highway along which goods, faiths, and diseases crossed the continent.
Run a band of grass five thousand miles across the middle of a continent, too dry to plow but perfect for the horse, and you build the deadliest cavalry on earth almost by accident. This is the Eurasian steppe, the grass highway that bred the conquerors of the world. For some three thousand years it threw mounted archers against the farming empires on its edges, from the Scythians to the Mongols, and the settled world could rarely catch them. The same open corridor carried trade, religions, and the Black Death from one end of Eurasia to the other. Gunpowder, cannon forts, expanding bureaucratic states, and settler frontiers finally narrowed the freedom of the steppe.