The correct answer is A. Opium Wars
The Opium Wars were two conflicts between the Chinese empire and the British empire. The first one lasted between 1839 and 1842 and the second one took place between 1856 and 1860. The causes of these conflicts were the commercial interests created by the British illegal traffic of opium in India and China and the efforts of the Chinese government to impose laws and control that commerce.
Since the British contraband of opium generated a great social problem in China, where a large part of its population became severely addicted to this drug, the Chinese government decided to ban the commerce and use of opium in all its territory. This affected directly the British commercial interests, therefore the United Kingdom started a military reprisal in order to re-establish the commerce of opium.
The Chinese defeat in both wars forced the Chinese government to tolerate the opium business. Moreover, the British coerced the Chinese to sign the Unequal Treaty, by which China ceded Hong Kong to the UK and opened several ports to international trade with Europe. This ended several decades of the Chinese policy of international isolation.
