The Opium war was from 1839 to 1842, it was between Britain and china. it all started when Europe wanted to trade with different countries. So when Great Britain went to India they found this plant well this drug. so then they went to china and since china didn't wanna trade with them. Britain though if we get them addicted to the drug then they gonna want ti all the time and they would agree trading with us. That actually worked but then the Chinese government notice what they were doing so he prohibited selling opium or using it. so then Britain got mad but they kept trying so they went to war with china and took over Hon Kong and that's how China and USA ,etc they trade with china now. It also helped china getting out there to learn from other and new things. And not only that's one of the reason why china is so advance with technology now . This war was called the Opium war because the opium plant was what stared the Chinese and Britain to fight since Britain wanted to trade so bad with china , but china didn't. But at the end Great Britain won because they had china addicted to the opium and they convinced china. Also they had better technology and weapons.The British had firepower . and they took control of the important island of Hong Kong. And China was also forced to legalize the selling of opium.