Waltz's initial contribution to the field of international relations was his 1959 book, Man, the State, and War, which classified theories of the causes of war into three categories, or levels of analysis.
Kontribusi pertama Waltz untuk ilmu hubungan internasional adalah buku Man, the State, and War (1959) yang membagi teori penyebab perang menjadi tiga kategori atau tingkat analisis.