Despite the Burney Treaty of 1826, the British gradually spread its influence in the northern Malay states. During the reign of HM King Chulalongkorn the Anglo-Siamese Treaty of 1909 was signed. Hearing it from a Thai perspective was both interesting and insightful. It was seen as Siam signing away its land to a foreign power, in the aim of achieving a greater goal of protecting its hinterland proper in the Chao Phraya basin. On the other hand, the Malaysian discourse states that it was an audacious, unilateral decision between the British and Siamese without consulting the sultans of the northern Malay states, whose subjects would be at the mercy of the agreement. The will of the people was thought to be inconsequential. With a quick flourish of the pen, Perlis, Kedah, Kelantan and Terengganu changed overlords from the Siamese to the British. They were then incorporated into the Unfederated Malay States (Negeri-negeri Melayu Tak Bersekutu).
Since the Malay states formally came together Persekutuan Tanah Melayu (Federation of Malaya) , and subsequently Malaysia, the relationship between the rulers of the Malay states and Thailand have normalised. The 14th Yang di-Pertuan Agong HM Tuanku Abdul Halim was due to embark on a state visit to Thailand last week on the invitation of HM King Bhumibol, but unfortunately it had to be cancelled due to His Majesty’s poor health.
Coincidentally, all of the most recent Yang di-Pertuan Agongs of Malaysia, as shown above, were from the northern Malay states, apart from Selangor.
Outwith of Malaysia, there is one other country which has a Malay sultan as its ruler, namely Brunei which has the official state ideology of Melayu Islam Beraja (Malay Islamic Monarchy). Thailand, comparably, holds on to the trinity of country(ชาติ), religion(ศาสนา) and king(พระมหากษัตริย์), as pillars of its society.