Pol Pot was literally China’s man in Southeast Asia. He was taught by the French Communists. Vietnam hated the French (past colonizers), and the Soviets backed the North Vietnamese - and the Chinese disliked the Soviets. Power balance thing within the Communists.

It rarely spilled over directly until Cambodia kept crossing over into Vietnam and murdering people when they got overzealous with their own internal murdering. Eventually Vietnam got fed up and stomped on them.

The CIA hated both of them with a passion.

You have no idea what the hell you’re talking about.