Good writing on postwar Korea is tough to find, to be honest. A lot of the most popular books on the subject are, quite frankly, crap - we would never tolerate the idea of someone claiming to be an expert on American history despite not being able to read or speak English, and yet there's an appalling number of books on modern Korea that were written by people without a working knowledge of Korean. Academic writing is little better, as the authors in the field that are most accessible to Westerners outside academia, Bruce Cumings and Charles Armstrong, are also the field's most reviled (Cumings for being too sympathetic to North Korea, Armstrong for being a serial plagiarist).

This thread in r/korea both contains and links to some good recommendations, though, and despite my caveat above, Cumings' Korea's Place in the Sun is still a great general overview of modern Korean history provided that you take it with a sizable grain of salt with regard to his pro-North Korea biases.