Preparing for War argues that, between 1815 and 1917, the US Army "went from a mode of informal direction grounded in the personality of the commander to a system of formal control using impersonal staff procedures" (2). This shift reflected changing views on the nature of military competence. Whereas early nineteenth-century officers were assessed based on their innate character and abilities, twentieth-century officers were expected to acquire a set, regulated body of knowledge. In Preparing for War,[1] former US Military Academy (USMA) professor and current active-duty Army officer J.P. Clark traces this change through four generations of officers, labeled foundational (pre-Civil War), Civil War, composite, and progressive. In terms of chronology, he chooses a middle ground between works devoted to longer[2] and shorter[3] periods of time. His thesis emphasizes that armies reflect the social and cultural values of their particular time and place.

Clark first surveys the debates between Federalists and anti-Federalists over military policy in the 1790s and early 1800s. The Federalists created a national army designed to act in concert with state militias. The war of 1812 demonstrated the limitations of this approach; the young nation's few successes in the conflict were secured principally by its Navy. Postwar reforms improved the Army's administration and organization, and the USMA at West Post produced a stream of trained officers, though deep divisions between line and staff officers persisted.

West Point graduates performed admirably in the Mexican-American War (1846–48), despite endemic personal rifts between senior commanders. The Army gained much from the experience of fighting Native Americans like the Seminoles in Florida. The war foreshadowed future tension between regulars and ad hoc volunteers. Clark astutely points out that the observers the Army sent to Europe mostly eschewed issues of strategy and policy, and concentrated on technical matters like fortification design. This predilection was evidence of the prevailing sentiment that military genius was innate and could not be taught or learned through observation.

Turning next to the Civil War, Clark maintains that the Army's overreliance on volunteers caused friction between regulars, who valued their strict prewar hierarchy, and volunteers, who saw their regiments as communal enterprises where, for example, officers could be elected rather than appointed. The war also exposed weaknesses in the officer preparation system:

The author highlights the career of Emory Upton, a regular Army officer who rose to brigade command and emerged from the conflict disenchanted with undue civilian involvement in military affairs and the inadequate prewar preparations of candidates for general officer positions. Many Civil War volunteers transferred into the regular army after the war, bringing with them a strong conviction that personal experience, not formal military training, produced successful generals. Emory Upton's fervent belief in professional military education put him in a distinct minority. Clark concludes that this divide was understandable, since volunteers-turned-regulars and regulars with little training could hardly be expected to support requirements for more education, thereby undermining their own positions and experience.

First at West Point and then at the Artillery School (Fort Monroe, VA), Upton tried to broaden the Army's educational system beyond technical subjects to strategy and policy. But subsequent commandants rolled back his curriculum changes. "This pattern of favoring immediate, tangible needs rather than the esoteric, abstract demands of a future war would continually reassert itself in American military professional education" (169). For instance, commanding generals Sherman and Phillip Sheridan ordered the schools at Fort Leavenworth and Fort Riley not to teach strategy.

Efforts to reform and modernize the Army floundered in the 1870s and 1880s because, Clark contends, progressives, disgusted with the nepotism and corruption of the Gilded Age, stressed regulation, accountability, and professionalism. But they lacked the political capital to institute military reforms before the 1890s and early 1900s.

Reform efforts also suffered from differing views within the Army about the very nature of military service. Prior to the Progressive Era, officers regarded their commission as a contract whereby the government provided lifelong employment in exchange for their service. They valued loyalty and solidarity over effectiveness or efficiency. In contrast, progressives believed military service should be evaluated primarily on the basis of the benefit the government derived. These diverging assumptions for a time stifled the nascent reform movement.

The Spanish-American War (1898) exposed the Army's deficient planning and staff work, especially in comparison with the Navy. The growing political and cultural strength of the progressive movement paved the way for the reforms of Secretary of War Elihu Root, which strengthened the National Guard, restructured relations between line and staff officers, and established a General Staff. The aftermath of the war brought more realistic large training exercises and the creation of the Army War College at Carlisle, Pennsylvania (1901).

However, the regulations written in 1910 and 1911 under the influence of the Root reforms were problematic. The 1910 regulations were inconsistent regarding the value of close coordination of artillery and infantry, a symptom of the Army's tactical confusion at a time of rapid technological change. The 1911 regulations failed to recognize the value of machine guns in defensive positions and artillery in support of infantry assaults. Clark argues that the new regulations failed to address "the central problem of preparing for war in the United States—devising the most effective means of employing hastily trained armies of citizen-soldiers" (226). Consequently, the Army went to war in 1917 under regulations that led to Gen. John Pershing's commitment to "open warfare."

The outbreak of World War I in 1914 did not bring any immediate organizational change in the Army. But, in 1916, the National Guard expanded and came under War Department authority. Furthermore, the Army and the administration of President Woodrow Wilson overturned a century of American military policy by mandating conscription in the event of war. The World War I Army did not rely on volunteer regiments and political generals as in previous generations. Moreover, it learned far less from (highly relevant) European experiences in 1914–17 than from the Russo-Japanese War (1904–5). Pre-First World War Army doctrine defined combat as a test of wills. This is apparent in Pershing's conviction that the trench-war stalemate was caused by British and French lack of aggression and vigor. His concomitant faith in "open warfare" tactics caused needlessly high American casualty rates in 1917–18.

J.P. Clark has clarified the backstory of a rich vein of military history scholarship. While the first generation of World War II histories focused on the Army's wartime performance, more recent scholars[4] have attributed its success to the education provided at Carlisle and Fort Leavenworth in the 1920s and 1930s. But Clark has gone further back in time, to show how the Army came to value professional military education to the degree it did over a century of change. In the process he has also spotlighted the grievous shortcomings of Pershing's open warfare tactics.[5] For these reasons, all students of the history of the US Army will benefit from a careful reading of Preparing for War.