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Research Questions

  1. How has the U.S. defense posture evolved over the nation's 200-plus years?
  2. What lessons can be drawn from this history as the United States plans for a future with new, yet somehow familiar, challenges?

Debates over the U.S. global defense posture are not new. As policymakers today evaluate the U.S. forward military presence, it is important that they understand how and why the U.S. global posture has changed in the past. Today's posture is under increasing pressure from a number of sources, including budgetary constraints, precision-guided weapons that reduce the survivability of forward bases, and host-nation opposition to a U.S. military presence. This monograph aims to describe the evolution of the U.S. global defense posture from 1783 to the present and to explain how the United States has grown from a relatively weak and insular regional power that was primarily concerned with territorial defense into the preeminent global power, with an expansive system of overseas bases and forward-deployed forces that enable it to conduct expeditionary operations around the globe. This historical overview has important implications for current policy and future efforts to develop an American military strategy, in particular the scope, size, and type of military presence overseas. As new and unpredictable threats emerge, alliance relationships are revised, and resources decline, past efforts at dealing with similar problems yield important lessons for future decisions. The author draws recommendations out of these lessons that touch on the importance of strategic planning; the need to think globally; the desirability of a lighter, more agile footprint overseas; and more.

Key Findings

Since independence, senior officials have developed and at least partially implemented seven distinct and identifiable U.S. global postures.

  • These were continental defense (1783-1815), continental defense and commercialism (1815-1898), oceanic posture and surge deployments (1906-1938), hemispheric defense (1938-1941), perimeter defense in depth (1943-1949), concentrated defense in depth (1950-1989), and expeditionary defense in depth (1990-present).

Three critical breakpoints stand out because of their enduring influence.

  • To protect U.S. overseas trade from predators, the U.S. Navy began to station squadrons of ships in key international waters.
  • The acquisition of territories in the Far East and Caribbean as a consequence of the U.S. victory in the Spanish-American War of 1898 both improved the ability of the nation to operate overseas and added a new justification.
  • World War II and its aftermath led to an enduring shift toward defense in depth, ensuring the security of the nation through a robust forward presence.

Host nations may agree to a U.S. military presence because they perceive a shared threat or in consideration of a transaction, such as payments.

  • If the perception of shared threat declines, the host nation may be less willing to tolerate the U.S. presence.
  • The U.S. military may have to leave or offer some sort of transaction to maintain the relationship.


  • Strategic planning continues to be critical.
  • A truly global perspective, driven from the top down rather than regional concerns alone, remains important.
  • Basing efforts inside and outside the continental United States should be connected.
  • The United States should adopt a posture that is more versatile and less costly, vulnerable, and conspicuous.
  • Moments when shared perception of threat is rising offer opportunities to expand presence in key regions.

Research conducted by

The research reported here was sponsored by the United States Air Force and conducted by RAND Project AIR FORCE.

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