1831. Another effort by Chaigneau in 1829 also failed. In 1831 another French envoy was turned away. Vietnam under Minh Mạng was the first East Asian country with whom the United States sought foreign relations. President Andrew Jackson tried twice to contact Minh Mạng, sending Edmund Roberts in 1832, and Consul Joseph Balestier in 1836, to no avail. In 1837 and 1838, La bonite and L'Artémise were ordered to land in Tourane to attempt to gauge the situation in Vietnam with respect to missionary work. Both were met with hostility and communication was prevented. Later, in 1833 and 1834, a war with Siam was fought over control of Cambodia which for the preceding century had been reduced to impotence and had fallen under the control of its two neighbours. In 1824, an Burmese envoy dispatched by Burmese king, presenting a proposal of a Burma-Vietnam alliance against Siam, which was immediately declined by Minh Mang. Minh Mang saw a risky war against Siam, the former ally, might have jeopardized Vietnamese hegemony in Cambodia, which had been acquired by his father Gia Long. Second, he had careful watched the British seizure of Singapore in 1819 and were waging war in Burma, thus he saw Britain as the new rising threat, and urged the Chakri dynasty of Siam should focus with Burma in their struggle against the British expansion. After Vietnam under Gia Long gained control over Cambodia in the early 19th century, a Vietnamese-approved monarch was installed. Minh Mạng was forced to put down a Siamese attempt to regain control of the vassal as well as an invasion of southern Vietnam which coincided with rebellion by Lê Văn Khôi. The Siamese planned the invasion to coincide with the rebellion, putting enormous strain on the Nguyễn armies. Eventually, Minh Mạng's forces were able to repel the invasion as well as the revolt in Saigon, and he reacted to Western encroachment by blaming Christianity and showing hostility, leading to the European powers asserting that intervention was needed to protect their missionaries. This resulted in missed opportunities to avert the colonisation of Vietnam through having friendly relations, since strong opposition was raised in France against an invasion, due to the costs of such a venture. After the outbreak of the First Opium War in 1839, Minh Mạng attempted to build an alliance with European powers by sending a delegation of two lower rank mandarins and