We are accustomed to thinking of French Indochina as the three mainland Southeast Asian territories France had carved out and controlled by 1893: Vietnam, Cambodia, and Laos. But, as early as 1885, French parliamentary Deputy Jean-Marie Antoine de Lanessan had presented a visionary geopolitical plan for a French imperium over a much larger area. This scheme would incorporate the entire Mekong River basin from upper Laos to the sea, including Siam’s northeastern (Isan) region, her rich Cambodian provinces of Siem Reap and Battambang, and her gulf port at Chanthaboun. Other “Siam activists” in France’s parti colonial, including her Minister at Bangkok in 1893, Auguste Pavie, went further and sought to establish a protectorate over all of Siam.

The economic system which de Lanessan envisioned was based on an interconnected series of lakes and rivers throughout the region, including the Mekong, the Tonle Sap, the Serpent River, and the Mun-chi River complex, which extended westwards to the city of Korat. This system might be seen as a Southeast Asian version of Rome’s mare nostrum – her inland sea, the Mediterranean – command over which guaranteed much of Rome’s power and prosperity. French control would also extend overland to connect Isan and Battambang with Siam’s gulf port at Chanthaboun. Siam itself, with its core zone in the valley of the Menam Chaophraya, would remain independent, but was expected to become a mere economic dependency of this expanded zone of French dominion centered on Saigon.

In 1891, de Lanessan was appointed Governor-General of French Indochina and, by 1893, with the “pacification” of Tonkin well underway, he moved to occupy the Lao east-bank territories. However, passage of the Mekong remained obstructed by the presence of numerous cataracts and exploitation of the lake and river system for commerce was hindered by the seeming inability of France’s own commercial interests to rise to this unique opportunity. In addition, the effort to extend French control westwards and south-westwards into Isan and Battambang faced numerous problems, including Siam’s own determined resistance, Britain’s opposition, and the changing climate of international politics. The result was that, despite France’s eventual garnering of some additional Siamese territory by 1907, de Lanessan’s vision of a French grand imperium in the Greater Indochina region was doomed to failure, and French Indochina as a whole never prospered to the extent hoped for. Siam, though deprived of substantial territory, escaped the worst French machinations and went on to become a remarkably prosperous and successful independent nation.