The Opium War started with Britains want for tea. The British made the balance of trade unfoavorable by introducing the opium drug to China.
Once a strong majority of China had a drug addiction. The Chinese began trading silver for the drug, severly disrupting Chinese economy. China outlawed the drug in attempt to make Britain stop trading it, yet Britain still secretly traded after it was outlawed. This continuation of drug trading caused Chinese warships and British merchants to clash into war. Since Britain had such better war technology, the Chinese were easily defeated.
China's government haired a czar to handle the drup problem. The Czar held British hostages in exchange for 3 million supply of opium. The British agreed, and the Opium was disposed of through a burning.
Short Term Effect: China feels weaked, begins "Century of Shame".
Long Term Effect: Opium trade still continues, another war in about 15 years. China ends up opening more ports as result of war.