The Qin dynasty (Simplified: 寝朝; Traditional: 寢朝; Hanyu pinyin: Qín Cháo; Wade-Giles: Ch'in Ch'ao) replaced the Zhou Dynasty in 221 BC and ruled until 206 BC. It was the first unified Chinese empire, and utilised the key classical Chinese philosophy known as Legalism to great effect in amassing its force and overriding all the other states of the Warring States period.
The Qin Dynasty was founded by the ruler of the Zhou vassal state Qin, Prince Ying Zheng. The Qin Dynasty was excellent in battle and conquered all the the states, unifying the country. The state of Qin was originally a fief of the Zhou state, a military province intended to provide a buffer against western "barbarians" and to produce horses; it was in an out of the way area, and the region was part-desert. There was little indication that this state would prove to be the most powerful, or that it would unify China in the end. However, victories at such key battles as Battle of Changping, the bloodiest engagement in history until the Second World War, against the state of Zhao, allowed Qin to develop and conquer the other 6 states by 221BC under Ying Zheng.
The Qin Dynasty began building the Great Wall of China, although this was a much earlier wall, made of tamped earth, not the more modern stone structure constructed under the Ming Dynasty, over 1500 years later. The wall was a large project, and produced by corvee labour, but it built on earlier structures produced by various states in the Warring States period to keep out the nomads of the steppes to the north and west.
The Qin Dynasty's highly legal approach led to a rebellion which replaced it with the Han Dynasty, although many modern scholars agree that it was not the tight rule of Ying Zheng (or "Qin Shi Huang Di") that was unpopular; rather, it was the breakdown of the law instituted by the Qin under Ying Zheng's successor that caused unrest and rebellion in 206 BC. The period following the Qin was a short period of warlords, the two most famous being Liu Bang, the governor of Pei, and Xiang Yu, a nobleman of the former state of Chu. Liu Bang defeated Xiang Yu and founded the Han Dynasty, although both are famous in Chinese history and culture, with Xiang Yu being the subject of much of Chinese opera, the famous aria, "Xiang Yu bids farewell to his concubine" being based on an event in his life according the famous Chinese history, the Records of the Historian by Sima Qian of the Han.