The Qin Dynasty () was the ruling Chinese dynasty between 221 and 206 BC. The Qin state was so named because its rulers were descendants of the first emperor"s ancestors whose fief was called "Qin". The Qin"s strength had been consolidated by Lord Shang Yang during the Warring States Period, in the 4th century BC. In the early third century BC, the Qin accomplished a series of swift conquests; the state subjugated the Chu, remnants of the Zhou Dynasty, and various other states to gain undisputed control of China.During its reign over China, the Qin Dynasty enjoyed increased trade, agriculture, and military security. This was due to the abolition of landowning lords, to whom peasants had formerly held allegiance. The central government now had direct control of the masses, giving it access to a much larger workforce. This allowed for the construction of ambitious projects, such as a wall on the northern border, now known as the Great Wall of China. The Qin Dynasty also introduced several reforms; weights and measures were standardised, as were other, more innocuous things. An attempt to purge all traces of the old dynasties led to the infamous burning of books and burying of scholars incident, which has been criticised greatly by subsequent scholars. The Qin"s military was also revolutionary in that it used the most recently developed weaponry, transportation, and tactics, though the government was heavy-handed and bureaucratic.