The major cause of the opium war was the high demand of opium in China. During this time, China and Great Britain were having some issues regarding the trades. Instead of paying silver, Great Britain had traded opium with China.
Because of this, Great Britain was able to pull of several treaties that allowed them to expand their trades in China and they were also able to have Hong Kong.
Because of these, China was forced to embargo some of the Opium Shipments and burn the opium coming in and out of the country. This event had angered Britain and thus, Opium War occurred
Peasants were clearnly not satisfied with Emperor Nianhao, the seventh emperor from the Ming Dynasty. The Taiping Rebellion was the biggest rebellion in China.