The Grand Illusion analyzes the impact of European military institutions on Hispanic America in general and examines the putative "Prussianization" of the Chilean army in particular. The authors focus on Chile's attempt to import and assimilate foreign military methods, doctrine, and materiel. They incorporate research from Chilean, Austrian, German, British, and American archives to offer a new interpretation of Chile's military reforms.

The authors argue that the Chilean army adopted only the most superficial aspects of the German military ethos, which eventually led to the creation of a large but ineffective army. The transfer of technology and doctrine failed because German institutions and policies did not suit Chile. Political infighting, greed, and corruption further encumbered the assimilation process. The authors findings call into question the widely accepted thesis that developed nations could and in fact did, change the nature of the military in developing countries.