China proper, about a thousand miles north to south and east to west, occupies much of the temperate zone of East Asia (Map 4.1). The northern part, drained by the Yellow River, is colder, flatter, and more arid than the south. Wheat and millet were the region’s most important crops. The dominant soil is loess — fine wind-driven earth that is fertile and easy to work even with simple tools. Because so much of the loess ends up as silt in the Yellow River, the riverbed rises and easily floods unless diked. Drought is another perennial problem for farmers in the north. The Yangzi (YANG-zuh) River is the dominant feature of the warmer, wetter, and more lush south, a region well suited to rice cultivation. The Yangzi and its many tributaries are navigable, so boats were traditionally the preferred means of transportation in the south.

Mountains, deserts, and grasslands separated China proper from other early civilizations. Between China and India lay Tibet, with its vast mountain ranges and high plateaus. North of Tibet are great expanses of desert, and north of the desert, grasslands stretch from Ukraine to eastern Siberia. Chinese civilization did not spread into any of these Inner Asian regions, above all because they were not suited to growing crops. Inner Asia, where raising animals is a more productive use of land than planting crops, became the heartland of China’s traditional enemies, such as the nomadic tribes of the Xiongnu (SHUHNG-noo) and Mongols.