US Air Force bombers like this B-52, shown releasing its payload over Vietnam, helped make Cambodia one of the most heavily bombed countries in history — perhaps the most heavily bombed.
To put 2,756,941 tons into perspective, the Allies dropped just over 2 million tons of bombs during all of World War II. Cambodia may be the most heavily bombed country in history.
https://gsp.yale.edu/sites/default/files/walrus_cambodiabomb...
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
It seems odd that the Vietnamese would expend much effort to keep the Khmer Rouge out of Thailand. Do you mean Vietnam's western border/Cambodia's eastern border?
