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.