A good writer, and unlike some of the others on this list, takes a broad-brush approach to his predictions, factoring in economics, history, environent, politics and some first hand observations.  Perhaps because he doesn't narrowly focus on one field of study, a fair number of his predictions, which are pretty pessimistic, have proved to be accurate.

I first read Kaplan back in the early 90s, and found his work interesting but too pessimistic. It was amazing to see just about everything he predicted-the spread of war in the Balkans; the collapse of Africa into chaos; the gradual decay of over-populated, badly-governed Islamic states, except Turkey and Malaysia; the globalization of Islamic terrorism; the dissolving Mexican/US border: all came true. Kaplan isn't always right-he was too pessimistic about China-but for the most part, his predictions were pretty accurate. Unlike most of the thinkers on this list, Kaplan tries to take everything into account: economics, politics, demographics, ideology, history; he uses interviews with both laymen and experts, as well as first-hand travel observations and secondary sources. Such a holistic method doesn't always work, but it seems to produce better results than extrapolating from a handful of facts and figures, as many Cassandras do.