In 1822, John Crawfurd carried out a mission to the court of King De l`Egem Rama II to determine Siam`s position on the Malay states.  The treaty confirmed the Siamese claims to the five northern states of the Malays, Kedah, Kelantan, Perlis, Terengganu – the future unfederated Malay states – and Patani. The treaty continued to guarantee British ownership of Penang and its trade rights to Kelantan and Terengganu without Siamese interference. The five Malaysian states were not represented in the treaty negotiations. In 1909, the parties to the agreement signed a new treaty, which succeeded that of 1826 and entrusted four of the five Malay states of Siamas under British control, with Patani remaining under Siamese rule.    Mongkut was convinced that his empire had to have full relations with Western countries in order to survive as an independent nation and avoid the humiliations suffered by China and Burma in the wars with Great Britain. Against the advice of his court, he abolished the former royal trading monopoly of goods and signed in 1855 the Treaty of Friendship and Trade with Great Britain. (This treaty, commonly known as „Bowring,“ was signed on behalf of Great Britain by Sir John Bowring, Governor of Hong Kong.) Under the terms of the contract, British traders could buy and sell without intermediaries in Siam, a consulate was established and British subjects obtained extraterritorial rights. Similar agreements were negotiated with the United States and France next year and with a number of other European countries over the next 15 years. These agreements not only offered free trade, but also limited the power of the Siamese government to tax foreign companies. The removal of these barriers has led to a considerable increase in trade with the West.
This expansion of trade, in turn, has revolutionized the Thai economy and linked it to the global monetary system. In the years that followed, Thai influence grew until it was challenged by Western powers. In 1795, the Thais seized the provinces of Battambang and Siem Reap in Cambodia, where the kings of Chakkri resisted Vietnamese invasions in the first half of the next century. The conflict between the Thais and the Vietnamese was finally resolved by a compromise providing for the creation of a common protectorate over Cambodia. The Thais also insisted on their claim to Suzerainty in the Malay state of Kedah, given the growing interest of the Empire for the peninsula. Following the Anglo-Burmese War (1824-26), Britain annexed territories in the region that had been contested for centuries by Thais and Burmese. This led to the signing of the Burney Treaty in 1826, an Anglo-Thai agreement that allowed British merchants to make modest trade concessions in the kingdom. In 1833, the Thais entered into a similar agreement with the United States.
On 6 June 1826 in Bangkok, Henry Burney, an agent of the British East India Company, signed for Great Britain and King Rama III for Siam.