Did America, at any point in history, do something to Cambodia (details inside)

I’m not asking this to provoke any strong feeling in anyone. I’m just genuinely curious about some random thing that I heard.

When I was spending my apprenticeship in Thailand, I met a Cambodian exchange student. A really outspoken and extroverted guy. He frequently hung out with us Vietnamese students for some reason, and he quickly became well-known among us. One night, I was sitting alone with him. I don’t exactly remember the details, but at one point he asked me what my favorite song was. I said it was Cassablanca and we searched for that song on Youtube. While the song was playing, he told me that the song was about a movie in America. Then he suddenly broke into a rant about how evil America was. I didn’t pay much attention because I was more focused on the song, but judging by the little that I heard, it seemed to me that he was angry about something America did to his home country. At that time I didn’t really take him seriously because of my presence on this site, and because his ranting was kind of incoherent.

I kind of forgot about the conversation until recently when I randomly heard the song Cassablanca again, and I suddenly remembered the conversation. Now I have been wondering about what exactly that guy said that night. I’m really curious because I don’t know anything about Cambodian history other than the Red Kmer, and I don’t think I have heard anything about America doing something bad to Cambodia in history. What could possibly riled him up so much that he derailed our conversation about a song? Was there something that happened in history that I somehow have never heard of?