At the same time, cavalry is gradually eliminated from the battlefield; matchlocks, flintlocks and eventually Smith & Wesson revolvers become dominant (they help Japan win the Russo-Japanese War).

In World War I, mustard gas, grenades, artillery and guns kill a massive number of soldiers that are buried in muddy graveyards on the Western Front.

In World War II, millions die on the Eastern Front because of Adolf Hitler's theories of living space (Lebensraum).

Keegan dedicates his book to an ancestor, a Lieutenant Bridgman in the Régiment de Clare, one of the Wild Geese mercenaries of the French Army, who was killed at the Battle of Lauffeld in 1747.

In a review in Foreign Affairs, Eliot A. Cohen wrote, "Despite some graceful writing and pointed observations, A History of Warfare fails to live up to the title's promise or the author's reputation".