 The Warring States period began 2500 years ago at the time of the invention of the crossbow.Needham notes that the invention of the crossbow "far outstripped the progress in defensive armor", which made the wearing of armor useless to the princes and dukes of the states.At this time, there were also many nascent schools of thought in China—the Hundred Schools of Thought (諸子百家), scattered among many polities.