Franco - Siamese War The Franco - Siamese War of 1893 was a conflict between the French Third Republic and the Kingdom of Siam . Auguste Pavie , French vice consul in Luang Prabang in 1886 , was the chief agent in furthering French interests in Laos . His intrigues , which took advantage of Siamese weakness in the region and periodic invasions by Vietnamese rebels from Tonkin , increased tensions between Bangkok and Paris . Following the conflict , the Siamese agreed to cede Laos to France , an act that led to the significant expansion of French Indochina . Context . The conflict started when French Indochina ’ s Governor - General Jean de Lanessan sent Auguste Pavie as consul to Bangkok to bring Laos under French rule . The government in Bangkok , mistakenly believing that they would be supported by the British government , refused to concede territory east of the Mekong and instead reinforced their military and administrative presence . Events were brought to a head by two separate incidents when Siamese governors in Khammuan and Nongkhai expelled three French merchants from the middle Mekong in September 1892 , two of them , Champenois and Esquilot , on suspicion of opium smuggling . Shortly afterwards , the French consul in Luang Prabang , Massie , feverish and discouraged , committed suicide on his way back to Saigon . Back in France , these incidents were used by the Colonial Party ( " Parti Colonial " ) to stir up nationalistic anti - Siamese sentiment , as a pretext for intervention . The death of Massie left Auguste Pavie as the new French Consul . In March 1893 Pavie demanded that the Siamese evacuate all military posts on the east side of the Mekong River south of Khammuan , claiming that the land belonged to Vietnam . To back up these demands , the French sent the gunboat " Lutin " to Bangkok , where it was moored on the Chao Phraya next to the French legation . Conflict . When Siam rejected the French demands , de Lanessan sent 3 military columns into the disputed region to assert French control in April 1893 . 8 small Siamese garrisons west of the Mekong withdrew upon the arrival of the central column , but the advance of the other columns met with resistance : in the north , the French came under siege on the island of Khoung , with the capture of an officer , Thoreaux ; while in the south , the occupation proceeded smoothly until an ambush by the Siamese on the village of Keng Kert resulted in the killing of French police inspector Grosgurin . Killing of Inspector Grosgurin . Inspector Grosgurin was a French inspector and commander of a Vietnamese militia in Laos . Like the French explorer and diplomat Auguste Pavie , he had been engaged in several exploratory expeditions in the region . He was a member of one of the French armed columns despatched in April 1893 by de Lassenan to cross the Annamite Range into the Laos area of Khammuan ( modern Thakhek ) and to occupy the disputed territory . The column was at first successful in evicting the Siamese commissioner at Khammuan by May 25 . Shortly afterwards on June 5 , the Siamese commissioner organized a surprise ambush on the village of Kien Ket , where Grosgurin , confined to his sickbed , had encamped with his militia . The commissioner had apparently been instructed by Siamese government representatives to " " compel their [ French troops ] retirement , by fighting , if necessary , to the utmost of their strength " " . The ambush resulted in the razing of the village and the killing of Grosgurin and 17 Vietnamese . The incident and the death of Grosgurin became known as the " Affair of Kham Muon ( Kien Chek ) " and was ultimately used as a pretext for the strong French intervention . Paknam incident . As a result , relations between Bangkok and the West soured , with France demanding reparations . The British sent in 3 navy ships to the mouth of the Chao Phraya , in case evacuation of British citizens became necessary . In turn the French went one step further in July 1893 by ordering two of their ships , the sloop " Inconstant " and the gunboat " Comète " , to sail up the Chao Phraya towards Bangkok , without the permission of the Siamese : they came under fire from the fort at Paknam on July 13 , 1893 . The French returned fire and forced their way to Bangkok . With guns trained on the Grand Palace in Bangkok , the French delivered an ultimatum to the Siamese on July 20 to hand over the territory , to withdraw their garrisons there , to pay an indemnity of two million francs in reparation for the fighting at Paknam , and to punish those responsible for the killings in the disputed territory . When Siam did not immediately comply unconditionally to the ultimatum , the French blockaded the Siamese coast . In the end the Siamese submitted fully to the French conditions , finding no support from the British . In addition , the French demanded as guarantees the temporary occupation of Chantaburi and the demilitarisation of Battambang , Siemreap and a 25 kilometre - wide zone on the western bank of the Mekong . The conflict led to the signature of the Franco - Siamese Treaty , on October 3 , 1893 . Franco - Siamese trial . Following the killing of Grosgurin , the Commissioner of the Kammuon District , Phra Yot , was acknowledged by his government to have been the responsible official , although was he initially acquitted of wrongdoing in a trial in March 1894 . A " Franco - Siamese Mixed Court " was subsequently convened in June 1894 . The court determined that Phra Yot had brought extra forces to surround the house in Kien Ket occupied by the ill Grosgurin , outnumbering his small Vietnamese militia ; that Grosgurin and those Vietnamese who had not managed to escape had been killed and the house subsequently set on fire on the orders of Phra Yot . In a joint agreement between the Siamese and the French , Phra Yot was condemned to 20 years of penal servitude . The solicitor for the defense was the Ceylonese lawyer William Alfred Tilleke , who was later appointed Attorney General of Siam and granted a peerage by the king . The Royal Thai Army fort Phra Yot Muang Khwan in Nakhon Phanom Province on the border between Thailand and Laos commemorates Phra Yot . Consequences . The Siamese agreed to cede Laos to France , an act that led to the significant expansion of French Indochina . In 1896 , France signed a treaty with Britain that defined the border between Laos and the British territory in Upper Burma . The Kingdom of Laos became a protectorate and was initially placed under the Governor General of Indochina in Hanoi . Pavie , who almost single handedly brought Laos under French rule , saw to the officialization in Hanoi . The French and the British both had strong interests in controlling parts of Indochina . Twice in the 1890s , the French and British were on the verge of war over two different routes leading to Yunnan . Two major difficulties stopped these two powers from war . The first was the geography of the land made it difficult to move troops efficiently and therefore would have made waging a war very costly and most likely ineffective . The second factor that kept the two countries apart was that they were both fighting a very difficult battle within their respective countries . Malaria was common and deadly . The routes that the two countries were interested in never really came into use . In 1904 the French and the British put aside their differences with the Entente Cordiale of 1904 , which ended their dispute over routes in southern Asia .