This paper clearly shows the immediate relevancy of historical study to current events. One of the most common criticisms of the U.S. plan to invade Iraq in 2003 is that too few troops were used. The argument often fails to satisfy anyone for there is no standard against which to judge. A figure of 20 troops per 1000 of the local population is often mentioned as the standard, but as McGrath shows, that figure was arrived at with some questionable assumptions. By analyzing seven military operations from the last 100 years, he arrives at an average number of military forces per 1000 of the population that have been employed in what would generally be considered successful military campaigns. He also points out a variety of important factors affecting those numbers-from geography to local forces employed to supplement soldiers on the battlefield, to the use of contractors-among others.