Ideological foundations are explained by different historians in different ways, but all of the 'big' works on the subject do this.

Kiernan suggests that it was predominantly a racialist style of thinking that produced certain ideological quirks, expanded upon to include fetishization of agrarianism, cults of antiquity and territorial expansion in his book Blood and Soil.

Short suggests revolutionary influence from French-colonial education, marxism-leninism-maoism-stalinism, as well as the particulars of theravada buddhism, a combination of all these may have been the primary influence on the CPK and Pol Pot.

Someone like Henri Locard in his collection of Khmer Rouge slogans also spells out the influence of Maoism and revolutionary thinking, which might be a handy resource for something like an exam. Easy to quote slogans and they are fairly explicit in their ideological underpinnings eg "with the Angka we will have a great leap forward a super great leap forward".

Hinton is another good historian for explaining the why... his book 'why did they kill?' and the essay's which formed it's foundation (that can be found on JSTOR I'm pretty sure) give a good look into the kind of psyche behind it.

For me, and as I've probably said in numerous answers I've made here on the topic, I generally go with the Philip Short style explanation - particularly if you are going to be talking about Pol Pot in particular. The biography he wrote, Pol Pot: History of a Nightmare is, in my view, one of the best books written on the subject.

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