Task: Question Generation
Input (English): Passage: Before the Monthon reforms initiated by king Chulalongkorn, Siamese territories were divided into three categories: Inner Provinces forming the core of the kingdom, Outer Provinces that were adjacent to the inner provinces and tributary states located on the border regions. The area of southern Laos that came under Siamese control following the Lao rebellion  and destruction of Vientiane belonged to the later category, maintaining relative autonomy. Lao nobles who had received the approval of the Siamese king exercised authority on the Lao population as well as the Alak and Laven-speaking tribesmen. Larger tribal groups often raided weaker tribes abducting people and selling them into slavery at the trading hub of Champasak, while themselves falling prey to Khmer, Lao and Siamese slavers. From Champasak the slaves were transported to Phnom-Penh and Bangkok, thus creating a large profits for the slavers and various middlemen. In 1874 and 1884, king Chulalongkorn enacted two decrees banning the capture and sale of Kha slaves while also freeing all slaves born after 1868. Those abolitionist policies had an immediate effect on slave trading communities. In 1883, France attempted to expand its control in Southeast Asia by claiming that the Treaty of Huế extended into all Vietnamese vassal states. French troops gradually occupied the Kontum Plateau and pushed the Siamese from Laos following the Franco-Siamese War. A new buffer zone was thus created on the west bank of Mekong, as the area lacked the presence of the Siamese military local outlaws flocked the newly created safe haven. In 1899, Siam abolished the tributes collected from vassal states, replacing them with a new tax collected from all able bodied men, undermining the authority of Lao officials. The combined effects of the abolitionist laws and taxation led the Lao and Kha  nobility into an open rebellion.
Output (English): Which event happened first, the Lao rebellion or when the French troops gradually occupied the Kontum Plateau?