AHC/WI: Siam under a Colonial Empire

How would you manage to get the strong Siam empire as a simple European colony like most of Asia? Bonus point if it is not either France or UK.
Lastly as this is also a WI, what would be the effects of such scenario? You can count with 1 hand every single vaguely independent Asian nation, plus what would the post-colonial border look like? The scenario that I have in mind is a Thailand divided between British and French with the former having everything south of Bangkok and the northern Shan land and the French everything else; so the scenario I have in mind is an independent Shan state instead of OTL Burma plus bigger Lao and Cambodia. Malaysia would gain a little of the Southern Thai land and Thailand remains with nearly no minorities outside oversea Chinese.
The earliest POD possible is 1815.
 
Perhaps a newly independent (in the 1830s) Philippines intervenes in the 1880s, flexing its power as Imperial Japan did with Korea?
 
Always imagined the Dutch first gaining trade relations with and then conquering Siam, as a balance against Spanish Philippines.
This may lead to the Dutch conquering a giant-ass part of Southeast Asia, with only a small tip of the Malay peninsula becoming British. Maybe Formosa becomes French.
 
Germany.

What really happened OTL-

In 1890 Britain exchanged Heligoland for Zanzibar with the Germans. In 1892 France and Russia signed a treaty of alliance (this in the middle of the "Great Game" between Russia and Britain over Central Asia). In 1893 France went to war with Siam (Thailand) and this upset Britain as it could have brought the French closer to the Indian border. Germany under Chancellor Caprivi wanted to secure Britain as an ally. This never happened, the Germans got disenchanted with Britain and angry; after the failed Jameson Raid to overthrow the Boer Republics in 1895 the Kaiser sent a telegram congratulating the President of Transvaal; pissing off the British. 1896 Kaiser says "“nothing must henceforth be settled in the world without the intervention of Germany and the German Emperor”, further pissing off the British.

What if instead-

1890 Heligoland-Zanzibar Treaty creates a better atmosphere in Britain towards Germany; this is the main PoD. Britain becomes nicer to Germany, Kaiser and the British King, being cousins, begin a good rapport and Caprivi is successful in good relations with the British. When France invades Siam, the British and Germans intervene, Germany gets a protectorate over Siam that evolves into greater and greater control (a la British in the Persian Gulf) and promises not to support in any fashion or recognize in any way the Boer Republics (which had quite a few Germans btw) in return.

This would of course cause butterflies that cause WWI to be radically different, but that wasn't the question. Just someone other than France or Britain.
 
Well, the late history of Siam is a double team game by France and the UK to fuck it up as much as possible without actually dismantling it, like when the UK promised protection against France and paid itself with the Northwest corner of the country without asking.

It's easier if it's France/UK so I'll go with that.

It's a beautiful day of 1890. A young ambitious marine lieutenant has been sent to "review" the Western frontier of the Laos protectorate. For reason x or y, excited Siamese troups shoot at him (maybe he reviewed the wrong side of the frontier, completely accidentally as young ambitious lieutenant in this time and place are wont to do) and he takes it badly. Oh boy.

He gathers his troups and local auxiliaries and goes on to the region of Trat to right his wrong. The local garnisons fall quickly (the first Western military school was OTL opened a few years later) but he still feels wronged. He embarks on gunboats and besieges Bangkok before the Résident Général in Phnom Penh had a chance to react. But don't worry, he'll send him a strongly worded letter later.

When gunboats arrive in the port of Bangkok, the British ambassador offers protection to Rama V, by proposing to act as a diplomatic buffer, threatening war if there is further intervention in the country. The young ambitious lieutenant weighs his option and says ok, if they part the country as it is. British ambassador shakes on it. The Treaty (Deveaux-Brenton) separates the Siam in three parts. Each province on the marshes will be integrated in respectively Bangladesh and Laos. The rest of the country will become a pseudo country like Egypt was, under heavy tutelage of both French and English advisors.
 
The Treaty (Deveaux-Brenton) separates the Siam in three parts. Each province on the marshes will be integrated in respectively Bangladesh and Laos. The rest of the country will become a pseudo country like Egypt was, under heavy tutelage of both French and English advisors.

I think you mean Burma and Laos. As Bangladesh (or more accurately Bengal at this point in time) is separated from any border with Siam by all of Burma
 
I think you mean Burma and Laos. As Bangladesh (or more accurately Bengal at this point in time) is separated from any border with Siam by all of Burma

I think you're right!

Damn, I knew I had something wrong in my frontiers, sorry about that!
 
The Treaty (Deveaux-Brenton) separates the Siam in three parts. Each province on the marshes will be integrated in respectively Bangladesh and Laos. The rest of the country will become a pseudo country like Egypt was, under heavy tutelage of both French and English advisors.
Isn't this basically OTL? Minus the pseudocountry part, but Thailand lost about half its territory to the UK and France. All of the land east of the Mekong became Laos, part of the west was incorporated into Burma, and the four southernmost provinces became part of what would become Malaysia. The Thai renounced control over Cambodia to the French in 1867.
 
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