The Taiping rebellion in China began in 1850 and was finally put down in 1864. It was led by a former school teacher who discovered, after repeatedly failing his civil service exams, that he was the younger brother of Jesus Christ, destined to bring China over to his own brand of Christianity.
The rebellion was by far the most destructive conflict in the nineteenth century. It illustrates a general characteristic of Chinese history: Chinese wars were fewer but more destructive than European ones. China was unified for most of the past two millennia, governed by dynasties which established peace for long periods of time, among a huge population, over a vast area. But when things fell apart in China, whether from invasions (usually involving steppe nomads) or internal rebellions, vast numbers of people died. Here’s a chart comparing estimated numbers of war deaths for major wars Europe (red) and China (blue) between 1 and 1800 CE.
The Taiping rebellion comes too late to show up on the chart, but cost the lives of about 20 million people.