The book's title is a reference to the means by which European nations conquered populations of other areas and maintained their dominance, often despite being vastly out-numbered - superior weapons provided immediate military superiority (guns), European diseases weakened the local populations and thus made it easier to maintain control over them (germs), and centralized governmental systems promoted nationalism and powerful military organizations (steel). Hence the book attempts to explain, mainly by geographical factors, why Europeans had such superior military technology and why diseases to which Europeans were immune devastated conquered populations.[