Competition among the Zhou fiefs had reduced them from sixty or so to only twenty by 480 BC. By 300 BC, there were only seven large and a few small ones left. The dukes one after another took the title of “King.” No longer feudal domains, they were territorial states with clear boundaries demarcated by long walls – walls that were not even meant to stop the fighting. For the point of the territorial state was to acquire more land and labor, usually through war. From 535 BC until 286 BC the Zhou states saw 358 wars, more than one a year. Different large states – Wei, then Qi and Qin -- rose to the dominant position and then fell, while small states desperately maneuvered between the horizontal strategy (allying oneself with one great power) and the vertical strategy (many small states allying together). Meanwhile, members of the ruling class within each state quarreled more and more violently with one another. As the rulers built themselves enormous above-ground tombs, their earthly power far outstripped that of their kinfolk. Another complication was that in many domains, ministerial families usurped thrones, and lords hired talented knights instead of assigning government positions according to heredity.
The fiefs had become states, and the basics of war changed. Until about 500 BC, war ran on bronze weapons, chariots, and warriors organized by aristocratic clans, in armies no larger than several thousand soldiers. Late in the Warring States period Qi, Qin and Chu could each field a million men, and 100,000 to 200,000 soldiers might take part in a single battle. Chariots surrounded by foot soldiers were replaced with cavalry and huge infantry units, carefully ranked and with specialist commanders. Instead of compound bows there were deadly crossbows, along with swords. Instead of wounding an enemy, or chasing an army back, the objective was to kill.
Along with walls, iron, horses, and slaughter, another great change was the slow appearance of a new social rank: commoners. In the feudal system they had been only an unnamed residual category of no political importance, a motley array of serfs working on the Zhou aristocratic estates, sixth-generation feudal sons cast off by the aristocracy, people who had been living in the Zhou lands before the conquest, and incorporated Di and Rong people. Now the kings were courting them to work new lands in the counties, and serve in ever-larger armies of infantry. Commoners began – slowly – to emerge into political view. A key reason for their rise was that iron weapons could arm far more soldiers.