Task: Question Generation
Input (English): Passage: In early 1765, a 20,000-strong Burmese army stationed at Kengtung, led by Gen. Ne Myo Thihapate, left Kengtung for yet another Burmese invasion of Siam. With the main Burmese army gone, Liu used a few minor trade disputes between local Chinese and Burmese merchants as the excuse to order an invasion of Kengtung in December 1765. The invasion force, which consisted of 3,500 Green Standard troops along with Tai-Shan militias, laid siege to Kengtung but could not match battle-hardened Burmese troops at the Kengtung garrison, led by Gen. Ne Myo Sithu. The Burmese lifted the siege and pursued the invaders into Pu'er Prefecture, and defeated them there. Ne Myo Sithu left a reinforced garrison, and returned to Ava in April 1766. Governor Liu, in his embarrassment, first tried to conceal what had happened. When the emperor became suspicious, he ordered Liu's immediate recall and demotion. Instead of complying, Liu committed suicide by slicing his throat with a stationery knife, writing as blood was pouring from his neck: "There is no way to pay back the emperor's favor. I deserve death with my crime". While this kind of suicide in the face of bureaucratic failure apparently was not unusual in Qing China, it reportedly enraged the Emperor nonetheless. Sorting out the Mien  was now a matter of imperial prestige. The Emperor now appointed Yang Yingju, an experienced frontier officer with long service in Xinjiang and Guangzhou.
Output (English): Which event caused Liu to commit suicide?