That said, it seems the bigger problem in Cambodia is landmines, and AFAICT most of those were buried during Cambodia's internecine conflicts by various domestic factions and by the Vietnamese. See https://www.halotrust.org/where-we-work/south-asia/cambodia, https://en.wikipedia.org/wiki/Land_mines_in_Cambodia, and https://www.dw.com/en/clearing-cambodias-leftover-land-mines... According to that last article a large number of them were planted along Cambodia's western border by the Vietnamese to keep the Khmer Rouge at bay. See https://en.wikipedia.org/wiki/K5_Plan