French colonial efforts to control the mountainous north west of Việt Nam remained thwarted until 1890 when they finally captured Đèo Văn Trị, White Thái lord of Mường Lay, who had been designated Governor of Lai Châu and Supreme Chieftain of Điện Biên Phủ and Tuần Giáo by the pragmatic Nguyễn court in Huế. As elsewhere in the north, the French moved quickly to graft their colonial administrative systems onto those already established by the Nguyễn court, ensuring Đèo Văn Trị's future co-operation by not only restoring his Mường Lay dominions but also awarding him the hereditary post of Supreme Thái Chieftain. A few years later work began to construct the colonial government headquarters of the new Lai Châu Province at Đồi Cao ('High Hill') in Lai Châu itself. The town also became an important military base, a development confirmed in 1905 when it was formally established as one of four north Vietnamese military territories (the others being Móng Cái, Cao Bằng and Hà Giang in the north east). An airstrip was subsequently constructed next to the Na River. After his death in 1915, Trị was succeeded first by his eldest son Đèo Văn Kháng and later by the most notorious member of the Đèo family, third son Đèo Văn Long (born 1890). On taking office in 1940 as Governor of Lai Châu and Supreme Chieftain of Điện Biên Phủ and Tuần Giáo, Long was also charged by the French government with overlordship of his younger brother Đèo Văn Mun's lordship of Mường Tè, his cousin Đèo Văn Ân's lordship of Phong Tổ and his Black Thái rival Bạc Cầm Qúy's lordship of Sơn La. By 1943 Long had even managed to secure the appointment of his nephew Đèo Văn Phủ as Governor of Bắc Cạn in the north east, making him a force to be reckoned with in the power politics of French Indochina. As the oppressive policies of the Japanese-backed Vichy government began to bite after 1940, the Việt Minh war of resistance got under way from its base in the Việt Bắc. When members of the French administration belatedly tried to resist the Japanese in March 1945, the Việt Minh took advantage of the ensuing conflict to seize control of Tuyên Quang, Hà Giang, Cao Bằng, Bắc Cạn and Lạng Sơn in the north east and several regions in the north west, including Sơn La, Nghĩa Lộ and Lai Châu. However, Đèo Văn Long had left for France before the Việt Minh arrived in Lai Châu, and he subsequently remained there for over a year, attending the Fontainebleau Conference in July 1946. He returned to Lai Châu in the wake of its regarrisoning by French troops later that year. Shaken by the events of 1945-6 and desperate to restore their shattered authority in the far north, the French sought new ways of guaranteeing the allegiance of leading ethnic minority leaders. They eventually resolved to offer the major ethnic groups a hitherto unprecedented degree of self-government by setting up a number of autonomous regions throughout the far north. In Lai Châu, Đèo Văn Long was accorded the title King of the 'Thái Autonomous Zone'. 'King' Đèo Văn Long is remembered with loathing by many older inhabitants of the Lai Châu area; by all accounts he was a tyrant who exercised absolute authority, striking fear into the hearts of the local people by occasionally having transgressors summoned to his Đồi Cao office and executed on the spot. The ruins of Đèo Văn Long's residence lie on the opposite bank of the Đà River from Đồi Cao, next to the Mường Tè road. During the latter days of French rule, as the security situation began to deteriorate throughout the north west, the French military presence in Lai Châu increased substantially; many older inhabitants of the town remember the large numbers of Moroccans, Algerians and Tunisians who were posted here between 1946 and 1953. The French were finally forced to abandon Lai Châu during the winter of 1953 on the eve of the momentous battle of Điện Biên Phủ; deserted by his colonial masters, a discredited Đèo Văn Long fled with his family, first to Laos and then to Thailand, whence he is believed to have emigrated to France and died in the early 1970s.