勤王運動
The Siege of Ba Đình (December 1886 to January 1887) in Thanh Hóa province was a decisive engagement between the insurgents and the French. The siege was deliberately willed by the Vietnamese resistance leader Đinh Công Tráng, who built an enormous fortified camp near the Tonkin-Annam border, crammed it full of Annamese and Tonkinese insurgents, and dared the French to attack him there. The French obliged, and after a two-month siege in which the defenders were exposed to relentless bombardment by French artillery, the surviving insurgents were forced to break out of Ba Đình on 20 January 1887. The French entered the abandoned Vietnamese stronghold the following day. Their total casualties during the siege amounted to only 19 dead and 45 wounded, while Vietnamese casualties ran into thousands. The Vietnamese defeat at Ba Đình highlighted the disunity of the Cần Vương movement. Trang gambled that his fellow resistance leaders would harass the French lines from the rear while he held them from the front, but little help reached him.