How were the Opium Wars an example of imperialism in China?
The Opium Wars are an example of a Western nation forcefully imposing its will on another country, in the name of empire - which is essentially imperialism.
For years, Britain and China traded goods with one another, but the trade was very lopsided in the latter's favor. Chinese merchants accepted only silver in exchange for things like tea, china, silk, and other unique Chinese products. Then, throughout the 18th and 19th centuries, Europeans began getting more aggressive about trade. Britain, especially, sought huge profits wherever she could find them, even if it meant cheating the other side. In India, Britain squeezed every dime possible out of the colony, going so far as to rule it directly. Meanwhile, India suffered several famines made worse by England's goal of simply making money and turning a blind eye to anything hurting profits.
India also provided the British with very valuable commodities, including the opium poppy plant. Opium, a powerful painkiller and base for many drugs, is derived from this plant. Britain, as the new owners to a windfall of opium plants, now needed to dump their product somewhere for cash. China proved to be the best option, since its population was huge and demand was high.
However, China outlawed opium, making it impossible to get it into the country - unless the sellers could bribe an official into letting them in. This actually worked at first, until the Chinese put an honest man in charge of stamping out the bootleg opium trade. Lin Zexu accepted no bribes and destroyed thousands of opium chests.
With nowhere else to turn, and unused opium piling up, the British declared war. Although the French also participated, the British were the ones who effectively crushed the Chinese with their modern weapons. They forced the Chinese to reopen the country to not only just the opium trade but to other European products and ideas too. By bullying China into doing its will, the Opium Wars are an example of British imperialism. This is what imperialism is, at its heart: exploiting another nation for extremely significant gain, while letting the foreigners suffer.