War Without Mercy is backgrounded by a bitter war between the United States and Japan during World War II. However, it frames the war largely as a race war perpetuated by the former, arguing that the US strategically utilized national support of the war effort to reassert Western primacy, particularly the primacy of American nationalist identity, over US-Japanese relations. Similarly, the Japanese side during the war sought to solidify public perception of the United States as a domineering Western evil.

The book uses a variety of sources spanning different mediums to illustrate the complex ways in which each country leveraged mass media and racial biases to rationalize committing atrocities against other humans. It arrives at the insight that war will probably always be the most crude and depraved tool humanity can fashion for absolving itself of its intrinsic fears and biases.