The Quiet American - Graham Greene
Greene's amoral tale of idealistic American agent Alden Pyle interfering with the war between the French and the Viet Minh has often been hailed as prophetic. It also happens to be tautly written, evocative and thematically complex.
Yes, the way it's framed around the competition between Pyle and an old Englishman for the affections of a child-like Vietnamese woman has racist and sexist overtones, but that's kind of the point - that for all their posturing and concern, neither of them every truly considers her capable of independent action.
Whether he meant it to or not, Greene's book would go on to become emblematic of the next half-century of American foreign policy.