The only thing stupider than your own customs are the customs of foreigners. This simple truth has spilt much blood.

The Queue Order (Traditional Chinese: 剃髮令; Simplified Chinese: 剃发令; pinyin: Tī Fà Lìng) was a series of laws violently imposed by the Manchu invaders of China in the seventeenth century.

Traditionally, adult Chinese did not cut their hair. According to the Classics of Filial Piety, Confucius said "the body, hair and skin, are inherited from one's parents, do not dare damage them. This is the beginning of filial piety." (身体发肤，受之父母，不敢毁伤，孝至始也。) Therefore both men and women wound their hair into a bundle or into various hairstyles. The Manchu men on the other hand shaved their forehead, leaving a long rattail called the queue.

When the Manchus broke through Shanhai Pass in 1644 (Chongzhen Year 17) they imposed the Queue Order in occupied territories, mandating that Chinese shave their head like the Manchus. This resulted in widespread resistance by the Chinese, and order was publicly revoked.

A year later, after the Manchus had reached South China, Dorgon reimposed the Queue Order, giving the Chinese 10 days to shave their hair into a queue, or face death. Their slogan was "Lose your hair and keep your head, otherwise, keep your hair and lose your head". The Chinese people resisted the order and the Manchu conquerors struck back with deadly force, massacring all who refused to shave their hair. The Three Massacres at Jiading and the Ten-day Massacre at Yangzhou are two of the most famous of such massacres, with death tolls at 50-200 thousand, and 100-800 thousand respectively. The imposition of this order was not uniform; it took up to 10 years for all of China to be brought under compliance.
-http://en.wikipedia.org/wiki/Queue_Order