Hong Xiuquan becomes a devout (and conventional) Catholic after being exposed to Italian and French missionaries. He retains his revolutionary fervor but never develops his bizzare syncretic beliefs. So, when he begins his rebellion against Qing rule in the 1840s and 50s, he is publicly supported by the Pope and Napoleonic France.
His rebellion, with its Christian support and progressive attitude, gains widespread popularity. The Hui muslim rebels join with Hong when they are promised religious tolerance in the new regime.
The French send military instructors and materiel to the rebels, and, when it appears clear that the Qing are collapsing, Russia invades from the north and captures most of Manchuria. Chinese settlers and some Mongols in inner Mongolia, as well as the Nien rebels in the north, join with Hong's rebellion, and after a swift northern expedition, Beijing is captured and the Qing surrender.
The Kalmyks in the east, with Russian help, also revolt, but during the crimean war, Russia is unable to aid the fledgling nation, which is attacked by Hong's China. The Kalmyks hold their own, but lose some territory in the peace that follows. Hong's China also expands into southeast Asia, annexing northern Vietnam and Laos with French approval.
In exchange for British recognition and cessation of the opium trade, Hong agrees to cede the island of Hainan to the British, and guarantee Thibetan independence as a British puppet state.
Hong declares the foundation of the Xiao (霄) Dynasty, and takes the era name Tianshun (天顺). He makes the official state religion Roman Catholicism, but allows freedom of religion in exchange for a small tax hike. He implements a program to liberate women, and bans, among other things, footbinding and arranged marriage. He does, however, keep many of the traditional Chinese social customs, and, outside of religious matters, encourages syncretism of Chinese and western elements. The flag of the new Christian dynasty is a buff saltire on a blood-red field, with the characters Da and Xiao in the upper and lower quarters.
In an historic event, pope Pius IX travels to China in 1873 to crown Tianshun emperor in a Catholic ceremony. This event cements ties between China and the papacy, as well as catholics across the world.