The two Opium Wars, fought from 1839-1842 and 1856-1860, have been understood by the Chinese as the beginning of their "Century of Humiliation" at the hands of Western powers, most notably Britain.
Early in the nineteenth century, an insatiable appetite for Chinese goods, such as tea, silk and china, led Britain into a trade deficit with China. To combat that, Britain significantly increased its opium trade with China. It used opium from India, which it controlled, to finance its purchases of Chinese goods. The Chinese government, seeing the extent to which opium addiction was affecting its people, decided to enforce its ban on the opium trade. In turn, England found excuses to go to war with China and easily defeated the badly weakened country. It then imposed harsh and humiliating treaties on the Chinese, which included payment of indemnities and forcing the Chinese to cede Hong Kong to the British. Although Britain, at the time the premier world power, spearheaded the effort, other Western powers also made lucrative inroads into China.
The Opium Wars could be seen as a moral low point for Britain in its zest to exploit the resources and peoples of other nations. The Chinese tried in vain to appeal to Queen Victoria to ban the sale of opium on moral grounds, and Gladstone, the British prime minister, decried the trade as evil.
The legacy of these two wars was years of distrust in China. In the latter half of the twentieth century, the country became communist and turned inward, taking control of its own destiny and growing into a major world power determined to protect its interests in Asia. The legacy also arguably impacted twentieth-century world politics: the English and French imposed similarly humiliating terms, the Versailles treaty, on the Germans after World War I, which did not go over well with Germany, and although the period of profitable imperialism was waning, Hitler waged war in part to build a similar empire to what the British had.
The Opium Wars are significant to history in general because of their significance for Chinese history.
In the Opium Wars, the British (and, in the second war, the French) forced China to make concessions to them. In the First Opium War, Britain gained Hong Kong as a territory and was given the right to trade in more Chinese cities than had previously been the case. In addition, the treaty that ended this war began the system in which foreign powers had the power of extraterritoriality in China. In the Second Opium War, even more cities were opened to European trade and Europeans were given more access to the interior of China.
These wars were important in the short run because they helped to expose the weakness of the Chinese government and to weaken it further still. This helped to eventually bring down the Chinese government and throw China into civil war. This civil war, which was interrupted by a long war against Japan, ended up bringing the communists to power in China.
The Opium Wars remain significant today because of their effect on China’s attitudes towards foreign powers. China remembers the ways in which it was humiliated in these wars and it distrusts foreign powers in part because it remembers how it was treated in the past. Therefore, these wars have helped to make relations between China and the West more tense than they might otherwise be.