In the years between 1758 and 1767, Burma moved once again against Siam and the rebellious Lao states, subduing Chiang Mai, Wiengchan, and Luang Phrabang. The Siamese, driven briefly from their capital at Ayuthaya in 1767, repulsed the invaders in the north in 1775, and subsequently sought a more secure hold over the northern frontier. That frontier included not only the Lao states of the middle Mekhong, but the fractious upland Tai chiefdoms. Between 1774 and 1788, Siam allied with the northern myang against the Burmese, and assumed nominal jurisdiction over the disunified Lao. Both Wiengchan and Luang Phrabang resisted domination encouraging frequent efforts at pacification by the Siamese. In 1778, Chao Taksin c Thon Buri despatched his general, Somdet Chao Phraya Mahakasatseuk (later Rama I, founder of Thailand's present Chakri dynasty), with an army of 20,000 against Wiengchan (Syamananda, 1981 : 97-98), whose chao had angered Taksin by ordering the execution of a rebellious minister of state who had assisted Siam in the annexation of Champasak. By 1780, the Siamese were engaged with Luang Phrabang and had occupied the Black Tai myang of Muoi and Than. During this campaign, a group of Black Tai families were taken captive, along with other Lao Tai, and marched south to settlements in what are now the Central Thai provinces of Saraburi, Rat Buri, and Chantaburi. A dozen years later, the Siamese-installed governor of Wiengchan sent troops into the highlands of myang Teng and Puan to quell rebellion, and additional Black Tai were impressed and relocated to Phet Buri province in Central Thailand (Burupaht, 1983).

Resettlement was not simply a punitive measure, but rather a military policy which reflected demographic realities and the prevailing concept of political jurisdiction Measuring political power in terms of control over areas of human settlement, leaders relocated potentially troublesome or historically recalcitrant peoples to areas more accessible to control. They depopulated disputed zones to preempt invasion, an thereby increased the size of the citizenry in regions where settlement might provide economic or military benefit to the state. Since the Tai rose to power in the great plain of the south, their kingdoms had suffered from underpopulation. The kingdom' economy and the wealth of its aristocracy depended upon farming revenues which along with canal-digging and other public works, were supported by a system of corvee and slave labor. Siam was also vulnerable to regular invasion from its neighbors ; Rama I instituted a policy of resettling war captives to defensive positions in the region around his new capital at Krung Thep (Bangkok). The policy's worth was proved in 1785 when the Burmese sought to invade Siam across its western border; emplacement of troops including Black Tai conscripts at Rat Buri, Phet Buri, and Kanchanaburi was decisive in repulsing and eventually routing the foreign armies.

Forced relocation of Black Tai continued for several decades and through many military campaigns directed by Siam against the Lao states and upland Tai myang. During the reign of Rama III, Chao Anuwongse of Champasak attempted to end Siamese rule over his native Wiengchan, taking the city and from there attacking Nakhon Ratchasima and Saraburi, north of Krung Thep, in 1827. The Siamese regained Wiengchan, lost it a second time when Annam came to the rebels' aid, and finally reoccupied the Lao capital with Chao Au as prisoner in 1829 (Vela, 1957 : 87). During this conflict, Siamese armies moved into Myang Teng and again took captives among the Black Tai, moving them to Phet Buri.}n 1836, a rebellion of three Black Tai myang against Luang Phrabang resulted in the relocation of additional captives to the expatriate Black Tai community west of Krung Thep ; unrest in the Sipsong Chao Tai encouraged enslavement again in 1838, 1864, and at various other times in the last half of the nineteenth century (Buruphat, 1983). Under Rama III (1824-1851), it is estimated that some 46,000 inhabitants of frontier and foreign locales were taken captive (Vella, 1957 : 78).

Siam faced recurrent problems of local unrest in the Lao and western Tonkin vassal states, aggravated by the rival claims of Annam, but had retained at least nominal allegiance from the northern chao since the beginning of the Chakri dynasty. During the reign of Rama V (1868-1910), Siam's hold over the middle Mekhong and Tai uplands was lost, not through rebellion or threat from its perennial rivals, but the westward expansion of French rule in Indochina. The Siamese Field Marshal, Chao Phraya Surasak Montri (Chamuan Waiworanart), sent by Rama V ostensibly to rid the frontier of Ho bandits---Chinese expatriates who moved in at the close of the Taiping rebellion against the Manchu in 1864---led the last Siamese campaign in the Tai uplands during 1887 and 1889. At Myang Teng, Surasak's army was met by Auguste Pavie, accompanied by several hundred troops of the French colonial forces. With French occupation a fait accompli, the Siamese field marshal attempted to impress upon the French representative the historical claim of Siam to the Sipsong Chao Tai and its peoples. As reported in a communiqué with Rama V, Surasak focused on Siam's heavy expenditure of lives in pacifying the feudal states, as well as the resettlement of Black Tai families to Phet Buri as points of argument with Pavie. He noted:

When Somdet Phra Nangklao Chao Ju Hua (Rama III, author) was graciously pleased to have those Black Thai establish a place to live at Myang Phet Buri, it was expected that Lao Song would have sons, grandchildren, and great-grandchildren, now numbering many thousands of persons. In raising the army for this campaign, many hundreds of able-bodied Lao Song men were also conscripted. And these men have met many relatives who live in Myang Thaeng, because the Lao Song/Black Thai people use patrilineages, in the fashion of the Chinese (Thatsanasuwaan, 1964 : 65, citing Montri, 1961 : 580, in Thai).