Final answer:
Hudson Taylor arrived in China during the Taiping Rebellion, a brutal civil war led by Hong Xiuquan, causing immense devastation and claiming millions of lives.
Step-by-step explanation:
When Hudson Taylor arrived in China, the disastrous event occurring was the Taiping Rebellion. This rebellion was one of the most devastating civil wars in history, leading to the deaths of approximately 20 to 30 million people. It arose largely due to the internal collapse caused by the opium crisis, the weakness of the Qing Dynasty, and the immense discontent among the peasantry. The leader of the rebellion, Hong Xiuquan, proclaimed himself the brother of Jesus Christ and sought to establish the Heavenly Kingdom of Great Peace by violently overthrowing the Qing Dynasty and eradicating Manchu influence and Confucian culture.