Siamese invasion of Kedah

The Siamese invasion of Kedah was a military operation mounted by the Kingdom of Siam against the Sultanate of Kedah in November 1821, in the area of what is now northern Malaysia.

Background
The East India Company took over the territories of Penang Island, which it called Prince of Wales Island, and then Province Wellesley on the mainland, from the Kedah Sultanate in the latter part of the 18th century. In return the Sultanate received payment, and some form of assurances of defensive help against the expansionist ambitions of the Siamese kingdom. The military and diplomatic situation in the area turned subsequently on the precise nature and effectiveness of the East India Company's commitment to defensive arrangements for Kedah against the Siamese.

18th century
The Sultanate and the Company had been engaged in discussions at least since 1771, when Sultan Muhammad Jiwa Zainal Adilin II had asked the Governor of Madras, at that time Josias Du Pre, for assistance against a rebellion. In 1772 a Company mission came to Kedah under Edward Monckton; but the conclusion was negative, to the effect that the Sultan planned aggression against Selangor to the south.

The Sultan of the time in 1786, Sultan Abdullah Mukarram Shah, sought from Francis Light assistance against threats to the Sultanate, comprising external problems from both Burma and Siam, and the possibility of disputed succession and internal weakness. The Burmese–Siamese War (1785–1786) had required of the Sultanate measures taken purely for expediency, including acknowledgement of Burmese overlordship, as well as the traditional Siamese overlordship. The Burmese had been campaigning in particular in Petani to the north of Kedah, an area then retaken by Siam. After the Fourth Anglo-Dutch War the Company was again interested in a base in the Penang region, to counter possible Dutch moves against the Straits of Melaka; and it was in 1786 that Francis Light was able to conclude a deal with the Sultanate on Penang Island. The Company's commitment to defensive arrangements appeared shallow to the Sultanate, and an attempt was made in 1791 to repossess the Island; which was successfully resisted by Light. From a position of strength Light, who was not authorised by the Company to guarantee the defence of Kedah, limited the understanding in the 1791 agreement to a less committal form of words.

Campaign
The Siamese forces of King Rama II achieved a rapid victory against those of Sultan Ahmad Tajuddin Halim Shah II. The campaign initiated a period of two decades in which Kedah resisted Siamese control. The Sultan took refuge on Penang Island, then under British control.

Aftermath
By 1822 there was a rise in the population of the British territories caused by an influx of Malays displaced by the invasion. The Burney Treaty of 1826 allowed the Siamese view of their rights to prevail.