Traditionally, Lanna forests belonged to the ruler of the nearest city. Anyone wishing to harvest logs needed the ruler's permission. Initially the Royal Court in Bangkok wasn't concerned, but as logging business increased problems arose. There were no fixed regulations; concessions overlapped, taxes weren't clearly delineated and little could be clarified through local courts. Rapid growth in the logging industry resulted in increasing timber value; the amounts concerned became substantial. Struggles related to overlapping concessions became frequent, demanding much legal attention. Strife, banditry and murder in border areas increased significantly. The British Government asked for help from the Bangkok central administration, which feared the British might attempt to take control of the area and hadn't the power to repel them.

In 1855, King Mongut (Rama IV) approved a Treaty of Friendship and Commerce with Sir John Bowring, direct representative of Queen Victoria (and the British Foreign Office, rather than of one of its Asian colonies or trading companies). Trade with Europeans had been closely restricted for the 1st half of the 19th century, but Mongut wanted friendship with Britain, and opened more concessions than had ever been given foreigners before. British subjects were even allowed to buy land and import opium; more importantly, they were put under an extraterritorial legal system (which in the event proved to be just for British nationals, instead of for all British subjects, as claimed). Siamese royal trading monopolies, except in opium, were abolished (Chinese businessmen bore the brunt of this loss, after less than 2 years). British subjects became answerable only to the British Consul in Bangkok. This was in accord with Southeast Asian maritime tradition, in which each community of foreign merchants, including Chinese, was under supervision of a top representative, with whom local leaders would deal exclusively.

Within the next seven years, similar treaties were made with France, the USA, Denmark, Portugal, Holland and Prussia. But Britain, because of Burma, was most significant. In 1868, Bowring helped make similar treaties to allow Siam direct relations with Belgium, Italy, Norway and Sweden (instead of with colonial officers), but Britain gained most. Singapore and Hong Kong sent regular ships, and the British Bombay-Burmah Corporation got the lion's share of teak.

Lanna's thick teak forests had interested the British since 1829, when British subjects came to Chiang Mai to purchase elephants, oxen and buffalo. The British had been establishing themselves in Burma since the beginning of the century, and by 1826 were well settled in (as part of British India) and starting after teak along the Salween River. Rama III allowed British commercial logging in the then economically listless Chiang Mai area, but as forests belonged to local leaders, problems naturally arose (as did the value of teak). After many misunderstandings, some British subjects were murdered. Bangkok, fearing the northern rulers could hardly deflect British military advances into their area, tried to balance British and Lanna perceived needs, largely with delaying tactics. A rift between Bangkok and Chiang Mai widened as the British constantly demanded compensation from Chiang Mai princes for losses due to lawlessness in the heavily forested frontier areas. As Siam modernized under Mongut, Chiang Mai become less isolated; for half a century, Lanna had enjoyed much autonomy, but with the arrival of a postal service (1883) and of international business, Chiang Mai found itself drawn more closely into Siamese politics.

Taxes from the principle cities of Lanna (Chiang Mai, Phrae, Nan, Lampang and Lamphun) included teakwood of an amount dependant on the size of the city. In addition to the annual tributes and taxes levied, Bangkok had the right to materials, especially teak, required for important ceremonies and construction. For this, the central government usually sent gifts in return, but in event of war, Lanna was required to send conscripts, without compensation.

Phra Chao Kawila (1781-1816) was followed by his brother Phraya Thammalangka (Chao Chang Phuak, ruled 1816-1821), who presented King Rama II with a white elephant and thus got promoted, becoming Phraya Chiang Mai Chang Phuak (Chao Chang Phuak). The third 'Jet Ton' ruler, Phraya Kham Fan (Chao Luang Sethi), ruled 1821-1825. Phraya Phutthawong (Chao Luang Phaen Din Yen, 'King of the peaceful Land' 1825-1846), fourth new ruler, administered the city longer, and with intellect rather than strength. During his reign the city enjoyed peace, in part because Burma was at war with the British, but also because he and his close, strong rivals in Lamphun and Lampang were all mutually afraid of the British. Towards the end of his reign Britain commenced trade and started to log teak along the border.

Rama V, to keep military disputes between Siam and British Burma from arising, established a system of bi-national courts and a Chiang Mai Royal Commissioner. In 1883, a second "Treaty of Chiang Mai" specified that British subjects could be heard only in international courts, or Consular Courts when more appropriate. Thus, the British opened a Chiang Mai Consulate (1883). From 1890 to World War II, about 20,000 logs were produced per year, cut to maximum possible length. After the war, until 1955, this resumed, but then there was partial nationalization, which became total in 1960 (under the Royal Forestry Department).

The first Governor of Mae Hong Son, Chankalea, appointed in 1874, was a Tai Yai. He was given the title Phraya Singhanartraja. In Mae Hong Son, the unique "Pan Soi" Shan architectural style, roofs built with multi-tiered cascades and embellished with fretwork, almost gives the appearance of gables upturned a bit at corners and ends (all really quite square), and remains common.

Burma became a British colony in 1886; this included the Shan States. Before the French took Indochina (including Lan Sang), T'ais had lost control of Chiang Rung; only China had the power to resist Burma there. Only the Siamese part of Lanna still had control of its own economic, political, social and cultural affairs, but was now paying tribute, including gold and silver trees, teakwood and military conscripts, to the Siamese Royal Court, and accepting increased commerce, influence and interchange with Bangkok.

As the teak-logging industry grew in the mid-19th century, officials from Bangkok became more and more important. Records indicate much resentment of abuse of power. Resistance to increases in Siamese hegemony remained fierce at least up to the death of Prince Kawiloros Suriyavong in 1870. Phraya Mahawong (Phra Chao Mahotara Prathet), the fifth of the Jet Ton lineage of Chiang Mai, ruled 1847-1854. There was warfare with the Burmese again, but logging increased, and Chiang Mai expanded territory and regional authority. In the reign of Kavilorot (Kawilorotsuriyawong or Chao Chiwit Ao, ruled 1856-1870), sixth ruler of new Chiang Mai, logging caused a backlog of lawsuits, mostly due to insufficient regulation. Kawilorot was a harsh ruler whose subjects suffered much corporal punishment, including many beheadings, but he refused to attend ceremonies honoring visiting Siamese princes, exchanged embassies with Burma, and kept the spirit ceremonies alive. After his death, annual ceremonies to ancestor spirits, at city pillars, ended, and Bangkok imposed direct control. During the next reign. Jao Intanon (IndraWichayanon, Chao Luang Ta Khao, 1871-1897) set up a school for girls (and another for boys). Intanon, the last independent ruler, had little power, but his wife, Chao Thep Kraison (Princess Tipkesawn), a daughter of Phra Jao Kawilorot, proved highly skilled in bureaucratic affairs, successfully assisting him for 13 years. Despite no formal learning, she and her sister, Princess Ubonwanna, were great traders, among the biggest in Siam. Women handled local trade, but only in the 1880s did they start learning letters - first taught by American female Presbyterian missionaries. Intanon and Tipkeson's daughter Chao Dara Rasami (or Rassama), at 13, in 1886, became a consort of King Chulalongkorn (Rama V). Rama V did wonders for Siam, but his regent Somdet Chaophraya Si Suriawong (Chuang Bunnag, 1868 to 1873, with continuing strong influence until 1883) systematically usurped Lanna power. As fully empowered king, Chulalongkorn incorporated Lanna into Siam (1892), and in 1908 made Dara Rassama Queen. Jet Ton ruler #8, Chao Noi Suriwongmekha became Jao Inthaworot Suriwong (1901-09), and through Queen Dara Rassami developed closer ties with Bangkok, bringing up musical and performing arts from there.

In 1884 mail service became regular - every two weeks. Before, international mail came through Moulmein, and for years after, private contractors carried much of the mail. The telegraph reached Chiang Mai sometime between 1885 and 1888. By 1905 there were (unreliable) telephones.

British subjects involved with logging in Lanna initiated too many lawsuits, and several were murdered; these problems had to be dealt with in Bangkok, as local commissioners lacked significant power. Administrative reform was unavoidable, and the 'monthon' (circle of administration) was produced, combining most Lanna city/states. Chiang Mai, Lamphun, Lampang, Phrae, Nan and Thoeng were made into Monthon Lao Chiang. Later, Chiang Rai and Mae Hong Son (established 1831) were put with Chiang Mai and Lamphun as Monthon Phayap, which became at 'monton thesaphiban' with royal resident commissioner in 1899. Nan, Phrae and Lampang became Monton Maharat, and Lanna schools became required to use only the central Thai alphabet and dialect.

When Lanna was annexed to Siam (1892), there were powerful British Consulates in Lampang, Chiang Mai, Chiang Rai and Nan. A forestry service was set up to reduce international legal complications, but the British remained rather more exploitative than co-operative. The Chao Muang hereditary rulers became but honorary figures; the last of the Chiang Mai nobility, Chao Kaew Nawarat, though called Chief of State, never had any administrative authority. His main function was to preside at certain spirit ceremonies. He died in 1939. The last prince of Lampang, Chao Boonyawat Wongmanit, died in 1922. Prince Maha Promsurathada of Nan died in 1931. The 9th and last Chiang Mai Prince ("Ruler"), Major General Jao Kaeo Nawarat was granted the surname suffix "na Chiang Mai" by Rama VI, for all Jao Jet Ton descendents. When Kaeo Nawarat died, his post was dissolved. The last prince of Lamphun, Chao Chakrakam Kajornsakdi, died in 1943.

At the beginning of the 20th century, tigers were still sometimes seen, even inside the major cities of Chiang Rai. The population of the area which became the present province had been reduced to about 5000, with perhaps 500 in the city at Doi Jom Tong. Chiang Saen City had about 70 residents; some of whom were wanted criminals. King Rama V ordered further resettlement, but malaria, hepatitis, and other diseases of swamps and jungle made for grave difficulties. Roads were poorly maintained: journeys from Bangkok to Chiang Mai took over three weeks, occasionally even three months. From Chiang Mai to Chiang Rai took about two weeks. The lengthy period of warfare had taken a toll still obvious a hundred years later, the Golden Age all but forgotten.