Siam first felt the pressure of Western expansionism during Mongkut's reign. Mongkut embraced Western innovations and initiated the modernization of his country, both in technology and culture—earning him the nickname "The Father of Science and Technology" in Siam.
Accounts vary about Nangklao's intentions regarding the succession. It is recorded that Nangklao verbally dismissed the royal princes from succession for various reasons; Prince Mongkut was dismissed for encouraging monks to dress in the Mon style.
Bunnak, with the supporting promise of British agents, sent his men to the leaving-from-monk-status ceremony for Prince Mongkut even before Nangklao's death. With the support of powerful nobility and the Great Power, Britain, Mongkut's ascension to the throne was ensured.
However, Mongkut did not abandon the traditional culture of Siam. In 1852, he ordered the nobles of the court to wear upper garments. Previously, Siamese nobles were forbidden to wear any shirts to prevent them from hiding any weapons in it and met the king bare-chested. The practice was criticized by Westerners and so Mongkut ended it.
Mongkut also improved women's rights in Siam. He released a large number of royal concubines to find their own husbands, in contrast to how his story has been dramatized. He banned forced marriages of all kinds and the selling of one's wife to pay off a debt.
In contrast to the previous king, Nangklao, Mongkut didn't see the importance of sending envoys to the Qing dynasty court, as the mission symbolised Siam's subjection to the Qing emperors and because the Qing dynasty was then not so powerful as it had once been, as it was itself threatened by Western powers.
The Europeans had been attempting to undo this monopoly for a long time but no serious measures had been taken. For Siamese people, trading with foreigners subjected them to severe punishment by the government. The taxation was partially reduced in the Burney Treaty. However, in the world of nineteenth-century liberalism, government control over trade was swiftly disappearing.
The abolition of such trade barriers replaced Siamese commerce with free trade. Import taxation was reduced to 3% and could only be collected once. This, of course, was a blow on the national revenue. However, this led to dramatic growth of commercial sectors as common people gained access to foreign trade. People rushed to acquire vast, previously empty fields to grow rice and the competition eventually resulted in the lands ending up in the hands of nobility.