2016 50 Book Challenge - Page 217
He writes about ancient warfare and modern international relations and conflict.
Back in the 1970s or 1980s, Luttwak wrote a book about Roman military organisation and fortification that was a bit controversial and which attracted quite a bit of discussion. He's also written quite a lot about the situation in the Middle East and South Asia over the past few decades, but he's not really taken that seriously as an international relations scholar.
I read an article a few months back on YC that indicated he is effectively a modern day Machiavelli. Very surprised to hear that he's not taken seriously.