He focuses on USA to the point of being boring now.

At this point nobody outside US believes any justifications to US foreign wars. If there was any willingness to believe any of that George W Bush pretty much trew in on a pile and set it on fire while doing stupid face.

Everybody knows USA just goes around the world and starts wars with whatever local evil they can safely engage (from geopolitical standpoint) to further their economical interests, both global and domestic.

It's not that the rest of the world is doing nothing because they believe any word USA puts out. It's because they can do nothing against current military and market hegemon.

Other countries will even happily pretend they believe US propaganda so they can calm their populace and keep themself safe from the next round of "democracy spreading" that comes out of US.

The US did indeed arm the "Khmer Rouge", whatever that is, after its era in power.

We know the Carter administration contemplated arming the Khmer Rouge and we know they hated the idea.

There is no evidence that they actually ever gave military aid.