During the mid-to-late 19th century, the British Government of India closely monitored the treatment of British subjects in Lanna, especially with the ambiguous boundaries near the Salween river affecting British teak businesses. The Bowring Treaty and the subsequent Chiangmai Treaties between Siam and Britain attempted to address these concerns but culminated in Siamese interventions in Lanna's governance. This interference, while intended to strengthen Siam's sovereignty, strained relations with Lanna, who saw their traditional powers being undermined. 

By the late 19th century, as part of Siamese centralization efforts, the traditional administrative structure of Lanna was gradually replaced. The Monthon Thesaphiban system, introduced by Prince Damrong, transformed Lanna from a tributary state into a direct administrative region under Siam. This period also witnessed the rise of European conglomerates competing for timber logging rights, leading to the establishment of a modern Department of Forestry by Siam, further diminishing Lanna's autonomy.

By 1900, Lanna was formally annexed into Siam under the Monthon Phayap system, marking the end of Lanna's unique political identity. The subsequent decades witnessed a few resistances to centralization policies, like the Shan Rebellion of Phrae. The last ruler of Chiang Mai, Prince Kaew Nawarat, served mostly as a ceremonial figure. The Monthon system was eventually dissolved after the Siamese Revolution of 1932. Modern descendants of Lanna rulers adopted the surname "Na Chiangmai" after King Vajiravudh's 1912 Surname Act.