Why has the institutional U.S. Army changed since the end of the Cold War? There is evidence that supports existing scholarly arguments that the civilian leaders caused important changes, which authors like Barry Posen (1984) and Graham Allison and Philip Zelikow (1999) expect. While analyzing changes in Army officers' personnel, education, and training systems, however, the preponderance of the evidence strongly suggests that the Army is changing itself--when it does change--providing further support to Stephen Peter Rosen (1991) and Williamson Murray and Allan Millett (1996). However, evidence suggests there are limits to what the Army will change itself, absent a change in its culture or priorities of its elite. Both shifts occurred during this study's time period: While evolving gradually throughout the 1990s, after experiencing difficulties in Iraq, the institutional Army transformed itself in ways that fundamentally changed the experiences for those involved.  This dissertation primarily tests four internal, three external, two U.S. Army specific cultural, and three organizational theory explanations for why organizations in general, and the U.S. Army specifically, has and has not changed from 1991-2007. I focus specifically on changes in the Officer Personnel Management System and the Officer Evaluation Report; the three Army combat training centers California, Louisiana, and Germany; and the U.S. Military Academy at West Point and the U.S. Army War College at Carlisle Barracks.  The evidence supports six important and cross-cutting findings. First, civilians are not fixing the military, even when problems arose. Second, despite its hierarchical structure, leadership priority and consensus were both critical in the Army making voluntary changes. Third, despite the oft-repeated claim by Posen (1984) and Allison and Zelikow (1999), there was overwhelming evidence that the Army changed itself without first failing. Fourth, evidence was less supportive of the institutional Army's willingness to incorporate experiential lessons that countered its culture. During this time period, it consistently prioritized changing itself in expectation of future threats. Fifth, major changes often occurred outside of bureaucratic constraints, in part because these changes to the formal systems were so difficult to make. Finally, there were real limits to the changes the Army could voluntarily make.  This dissertation concludes with specific institutional recommendations for civilian and military leaders and scholars to help continue the major changes being implemented since 2005-06.