Phraya Chakkri (hereafter to be styled as King Rama I) had scarcely assumed his new dignity when Bodaw Phra, King of Burma, attempted a new conquest of Siam. King Rama's military ability was such that the Burmese were finally everywhere defeated and, with the abandonment of Mergui and Tavoy by the Siamese in 1792, the recurrent wars between the two powers may be said to have ended for good. With the foreign danger averted, the King was able to organize his government, the seat of which was transferred from Tonburi to Bangkok, on the left bank of the river, where he constructed a fortified city.

Rama II became involved in war at the beginning of his reign. In 1786, the regent of the now effete Kingdom of Cambodia had formally recognized Siamese suzerainty and had sent the infant King to reside at Bangkok, while he continued to rule the state under Siam's aegis. Annam, to the east, however, made identical claims to supremacy and when, in 1809, the Annamese King attempted to enforce his demands, an army was sent from Bangkok to repel him. The brief campaign ended with Rama's annexation of the Cambodian province of Phratabong, while the rest of the country became a dependency of Annam.

Upon this King's death in 1825, the throne was usurped by one of his sons by a lesser wife, while the legitimate heir, Chao Fa Mongkut, a young man of twenty-one, retired to the safety of the Buddhist monkhood. The reign of Rama III is chiefly notable for Siam's resumption of political relations with the nations of the West. In 1833, a treaty drawn up between Siam and the United States of America represented the first formal tie between this country and any Asiatic power.

Toward the end of the reign, Cambodian politics again caused bad blood between Siam and Annam. A youth named Norodom, a son of the Cambodian King, had some time since been brought to Bangkok and reared at the Siamese Court. Upon his father's death, he was declared by Siam to be the rightful heir and, supported by a Siamese army, returned to Cambodia to gain the throne and, despite former agreements, to place the country again under Siamese protection.

During his years of retirement, Chao Fa Mongkut, the King's half brother, had assiduously devoted himself to the study of the English language, the sciences, and the manners, customs, and systems of government of foreign lands; at the same time, he missed no opportunity to meet and converse with European travelers. Coming to the throne as Rama IV in 1851, at the age of 47, he brought to his task a remarkable degree of enlightenment, which resulted in throwing the country open to foreign trade and intercourse, in the introduction of such arts as printing and shipbuilding, in the construction of roads and canals, in laying the foundations for systems of education and public health, and in numerous other reforms directed toward increasing the public welfare. His love of learning was indirectly responsible for his death for, visiting a mountain peak to observe an eclipse in 1868, he contracted the illness from which he died in that year.

The program of modernization initiated by King Rama IV was continued and expanded by his son, the great Chulalongkon (Rama V). Among the important reforms instituted during this reign were the abolition of debt slavery, the establishment of law courts, the construction of railways, the spread of education, regulation of the conditions of military service, and radical changes in methods of revenue and rural administration. The appointment of trained officials under organized control in place of ignorant provincial governors and hereditary chieftains welded the loose agglomeration of feudatory dependencies into the modern, homogeneous state.

In the year 1863, Norodom, whom Siam had placed upon the Cambodian throne, made a treaty with France, now master of Annam, by which he accepted French protection; at almost the same time he made an exactly similar compact with Siam. Thus each country found itself responsible for the protection of Cambodia against any possible aggressor, while each was given the sole right of dictating the foreign policy of that state. So absurd a situation could not last and, after 4 years of negotiation, Siam was compelled to yield to the French thesis of their superior rights as successors to the Annamese kings, to abrogate her treaty of 1863, and to abandon all claim to suzerainty over Cambodia.

Soon after Siam's withdrawal from Cambodia, the unofficial advocates of colonialism in France began to advance the idea that certain Siamese provinces east of the river Me Khong, having at one time formed a part of Annam, should be restored to that Kingdom, now a French protectorate. There is no historical basis for this claim, which was at first unsupported even in Paris, but when the colonial party added the argument that the unnavigable Me Khong, as one of the future trade routes of Southwest China, must at all costs be acquired by France, the French Government formally demanded of Bangkok the provinces in question. The Siamese replied by suggesting that the disputed territory be regarded as neutral until such time as the frontier could be properly demarcated and this was agreed upon but merely led to further trouble, each side accusing the other of violating the compact. Siam asked for arbitration, which was declined by the French. When, in 1893, bloody collisions occurred along the border, French gunboats, dispatched from Saigon, ascended the Chao Phraya, despite efforts of the Siamese naval forces to bar the way. In consequence of Siamese resistance, the French greatly increased their demands, now insisting that Siam give up all territory east of the Me Khong (including about half of the rich province of Luang Phrabang, to which no French claim had ever previously been laid). After 10 days of blockade, the Siamese had no choice but to accept a humiliating treaty which, among other concessions, required immediate evacuation of her eastern outposts and the payment of an indemnity; as a guarantee, France established a military occupation of the southeastern province, of Chanthabun, which was to continue long after all the terms had been fulfilled.

Relations between the two countries were far from improved by this episode and, during the following years, abuses in the exercise of French extraterritorial rights were a fertile source of provocation. In fact, despite every effort to avoid unfortunate incidents, the Government of Siam found itself spending all its energies in replying to diplomatic representations and to demands for inquiries, explanations, and reparations.

As the French demands increased in numbers and severity, there was no longer any question that Siam's national survival was at stake. But, in 1896, Great Britain, at last alarmed by France's growing strength in southern Asia and unwilling to have her approach too near the eastern confines of India, intervened. High feelings were aroused in both countries but, after lengthy negotiations, an agreement was concluded in the same year, by which Siam's autonomy was guaranteed that she might serve as a buffer between the rival empires.

Thereafter, relations between France and Siam tended to improve. It was not, however, until 1907, that, in return for yet another "rectification of the boundary," the French agreed to revise their extraterritorial rights and to remove the garrison from Chanthabun. A second convention of the same year resulted in Siam's restoring to Cambodia the province of Phratabong, which she had held since 1809, and receiving in exchange a part of the territory yielded in 1904 and obtaining a recognition of Siamese jurisdiction over Asiatic French subjects. Altogether, in warding off the European neighbor, Siam had been compelled to sacrifice no less than 90,000 square miles of her eastern lands.