If there were only one word to describe Eric Hammel’s How America Saved the World (Zenith Press 2009, 400 pages), it would be “comprehensive.” Mr. Hammel has thoroughly researched, meticulously compiled and brilliantly organized the development of the United States military during the period between the two world wars and thus created an essential book for all advanced students of the Second World War. At the dawn of World War II, America was most certainly a sleeping giant. In How America Saved the World, Mr. Hammel teaches us how the USA got to that point. Following World War I, the United States began a steady reduction in the size of its military forces. Increasingly a pacifist country, especially under the Hoover administration, the United States adopted a general policy of maintaining a purely defensive military. As a result, over the course of the decade following the Armistice, the US military largely became obsolete when compared to other more modern military organizations. Indeed, proponents of change and modernization (e.g. Billy Mitchell) were often blocked from promotion or forced out of the military altogether. During the 1930’s, the fate of the US Navy improved somewhat with the election of President Roosevelt but even a pro-Navy President could do little to help modernize the Navy with the USA and the world in the grips of the Great Depression. It was not until Keynesian economics began to take hold in the late 1930’s that proponents of a stronger US military could really find the necessary traction to begin developing a modern American military organization. Mr. Hammel presents his readers with an encyclopedic exploration of all of the factors that contributed to the decline of the US military and its subsequent Renaissance in the years between the two wars. He explores the dilemma that military planners faced in trying to both maintain their organizations in some form of military readiness while at the same time spending money on new and rapidly evolving technologies. He examines the effects of international treaties, such as the Naval Disarmament Treaties of 1922 and 1930, and domestic laws, such as the Neutrality Acts of the mid-1930’s, and how they served to paralyze the development of the US military capacity that the country would need so much during World War II. He considers the personalities who shaped policy during the intra-war years, from Hoover and Roosevelt to Marshall and Arnold and others. He analyzes the prevailing military technologies and the decisions made with respect to them. In short, Mr. Hammel considers just about every facet of US military development from 1918 to 1941, and he does so with scholarly focus and analysis. Yes, Mr. Hammel covers everything in one very tight volume. Unfortunately, the all-encompassing nature of How America Saved the World leads to its few flaws. Because the Mr. Hammel tries to cover so much material, his book is very dense. Admittedly, it is dense in a good way because it is so full of information, but the recitation of so much information at times makes it difficult to retain all that Mr. Hammel offers. Also, because the effects of certain events are felt in different ways by different organizations, there are times when Mr. Hammel has to repeat certain information in order to re-establish context as he moves from one branch of the military to another. Flaws aside, How America Saved the World is a brilliant work and it should be read by all serious students of World War II who have ever wondered how the USA could go from being the 17th strongest global military organization in 1941 to the strongest and virtually unchallengeable global military power in 1945. Although Mr. Hammel has not given his readers “light” reading, How America Saved the World is original, thought-provoking and insightful, and certainly well worth the time of every veteran student of World War II.