As the drawdown in defense spending starts to take effect, the Department of Defense's ability to maintain the readiness of its military forces is the subject of growing debate. Both civil and military leaders express deep-seated concerns about the impact on national security of defense cuts imposed by the Budget Control Act of 2011 and the March 1, 2013 sequestration. In the past, policy makers have tended to over correct with military drawdowns, thereby paving the way for military missteps. United States policies and defense strategies have historically left the military unprepared for the next conflict following drawdowns. The trajectory of defense spending since 9/11 is fiscally unsustainable despite an ever changing environment that is less secure, as a major drawdown of defense force structure is on the horizon. President Barack Obama warned that "we can't afford to repeat the mistakes that have been made in the past - after World War II, after Vietnam - when our military was left ill-prepared for the future." The question remains is how to accomplish this drawdown without hollowing the force. The purpose of this thesis is to illustrate through case study analysis relevant historical insights from past post-war military drawdowns that should be applied to current budget decisions in order not to end up with a "hollow force" incapable of executing the National Security Strategy. The author concludes that historical lessons from past post-war drawdowns provide a framework for planning the U.S. force structure of the 21st Century.