In the 1860s, the British invaders in Sikkim started to build roads and bridges leading to Tibet. They also sent recruited vagrants across Rina by the Tibet-Sikkim border to Mount Lungdo to explore paths. When they were spotted, they were stopped by locals. The British then sent people to the area north of Mount Lungdo, building roads and blockhouses. In the face of the imminent British invasion, the Gaxag government, in disregard of the compromising policies adopted by the corrupt Qing court, dispatched troops to Mount Lungdo, where they put up barriers and built blockhouses by which stood statues of Buddhist guardians. The British claimed this constituted a Tibetan invasion of Sikkim and told the Qing court that the Gaxag government of Tibet must withdraw its troops from Mount Lungdo in a given period of time or the British would station troops there too. In the face of the arrogant British, the Qing court, which feared border wars, decided to "Suffer wrong in pursuit of the overall general interest." It demanded the Gaxag government of Tibet withdraw its troops from Mount Lungdo.

The Gaxag government and the three major monasteries refused to do so by pointing out that Mount Lungdo was Tibetan territory instead of the Sikkim territory. Qing Dynasty High Commissioner Wen Shu saw through the British intentions and supported the Gaxag government in their fight against the British. While sowing bad blood between the Qing court and the Gaxag government, the British did their best to win over the Qing court in a joint political fight against the Tibetans, who stood for resistance against the British. In the meantime, the British massed some 2,000 troops south of slopes of Mount Lungdo, ready to launch an attack northward. On the Tibetan side, two Duiboin generals were sent to lead 900 Tibetan troops, and the militias were mobilized. They were deployed on Mount Lungdo and to its north. Galoon Lhalu Yexei Norbu Wangqu was appointed the chief commander.

On March 20, 1888 (the seventh day of the second month of the Tibetan calendar), the British troops attacked the Tibetan troops at Mount Lungdo. Tibetan official Doje Renzin and the Tibetan troops and militia rose to resist, killing some 100 British invaders in the first battle. They suffered from heavy losses in the ensuing battles and were forced to retreat to Yadong and Pagri, leaving Mount Lungdo in the control by the British. The Qing court dismissed Wen Shu, the Qing High Commissioner stationed in Tibet, who had supported the Tibetan struggle against the British invasion, and appointed obedient Sheng Tai to take his place as the Banbai Minister. In disregard of obstructions from the Qing court, the 13th Dalai Lama and the Gaxag government of Tibet mobilized some 10,000 Tibetan troops and militiamen and battled the British invaders from June through October, in an attempt to recover Mount Lungdo.

Following the instructions from the Qing court to the letter, the new High Commissioner stood in the way of the Tibetan troops and militia. This, plus the poor equipment of the Tibetan troops and militiamen, led to failure. The British troops crossed the Zhelilha mountain pass, and penetrated Rinqengang and Chunpi in Yadong. There, they kidnapped and put under palace arrest the Sikkim king then living in Chunpi. At that time, Sikkim maintained such good ties with Yadong of Tibet that the Sikkim king spent winters in Gangtok, now capital of Sikkim, and summers in Chunpi of Yadong. According to An Outline of Tibet written by the Japanese scholar Y. Narita, who reached Yadong and Mount Lungdo in the post-war period, stated: "When I passed that place, my servant said pointing at the old battlefield: During the battles two years earlier, dead bodies littered the ground and blood converged into streams. Bones were piled into hills. Alas! This tells of the causalities suffered by the Tibetans!" (Ya Hanzhang: Biography of the Dalai Lama, p.103)

As the year 1888 was the Year of Earth Mouse on the Tibetan calendar, the Tibetans refer to these battles as the War of the Earth Mouse Year.

After the end of the first British invasion of Tibet, the decadent Qing court yearned for peace talks with the British. In the winter of 1888, the Qing court sent Sheng Tai to Yadong to negotiate peace with the British. Under British pressure, Sheng Tai retreated step by step, seeking peace through the sale of his country. He joined British Indian Viceroy P.C. Lansdowne to sign the Anglo-Chinese Convention Relating to Sikkim and Tibetan Calcutta in 1890, which obligated the Qing government to recognize the British government's protectorate over Sikkim, formerly under the jurisdiction of China's Tibet.