Britain, after being denied trade from China, smuggled in opium from India on a large scale. The conflict grew violent when the British fleet destroyed a Chinese blockade and occupied Canton, China. This Chinese, in return for the British leaving agreed to allow Britain to trade. Later, Britain rekindled the conflict (this time accompanied by France) with the hopes of expanding their trade rights.
China before the conflict was entirely self-sufficient, and was resisting trading with the European as many European countries wanted Chinese goods
Reaction by Chinese: The Chinese resisted the import of opium, going so far as destroying 20,000 chests of opium in one month. Later they started physically stopping Britain from entering with blockades
Role of Europeans: Britain and France both fought in theses wars with the hopes of trading with the Chinese.
Significance: These wars ended China's economic isolation and introduced Chinese goods to Europe.