Opium Wars
Early in the 19th century, British merchants began to take opium into China in return for bringing Chinese tea back to Britain. In 1839, China said that the British could not bring opium into their country, so the British did not tell China about the opium they had brought with them.  Chinese officials found a lot of opium in Canton, a part of southern China which is now called Guangzhou, and destroyed it. The British were upset at this and sent gunboats in 1840 to attack Chinese cities along the coast. China had no weapons to protect themselves, and so they lost the war.