|Bas-Relief of Slaves, Angkor, Cambodia|
Cambodia's population in the 1880s was approximately 900,000 people. It has been estimated that 150,000 of those were slaves.*
Some of that number were hereditary slaves while others became slaves to pay off a debt.
French efforts to stop slavery were stymied by the Cambodian attitude to slavery; since it had been part of Cambodian life from at least as early as the pre-Angkor era it was seen by most Cambodians, and even the slaves themselves, as a normal, natural part of life.
King Norodom Ӏ wouldn't initiate French calls for the abolition of slavery despite several times agreeing to do so, and it wasn't until early in the reign of the more compliant King Sisowath Ӏ (ruled 1904-1927) that the French colonists had their way.
* In A Short History of Cambodia, John Tully