If national strategy defines US intent in its approach toward global affairs and provides focus for American foreign policy, then the US global defense (military) posture reflects the US capability to project military power beyond its borders and across transoceanic ranges in support of US national security policy objectives. The United States thus adopts and maintains a global military posture as an indispensable means of securing its national interests.
While national strategy can change from administration to administration, making major adjustments to the US global defense posture is much more difficult and time-consuming process. As a result, once made, adjustments to US defense postures have proven to be quite durable, enduring for tens of decades. Indeed, between 1783 and 1989, the United States assumed only three distinctly different global defense postures, each one tailored to a unique national security era:
• In the Continental Era, which extended from the birth of the Republic to about 1890, the United States adopted what might be best called a Naval Expeditionary Posture.
• In the Oceanic Era, which spanned nearly six turbulent decades between 1890 and 1946, the US assumed a Service Expeditionary Posture, which included for the first time several exterior bases, almost all sovereign bases located on US-controlled territory in either the Pacific or Caribbean Basins.
• The Transoceanic Era, marked by the long Cold War with the Soviet empire, stretched from 1947 through the fall of the Berlin Wall. During this period, the United States adopted a Garrison Posture which saw the basing of large numbers of combat troops on foreign soil.
Since 1989, the US has been slowly transitioning to a new global defense posture tailored to the unique demands of the post-Cold War world, which might best be viewed as the Second Transoceanic Era. The relatively slow development of this new global defense reflects, in large measure, the great uncertainty and lack of defined threats that characterized the decade immediately following the implosion of the Soviet Union. Now, however, as the national security challenges facing the United States have become more fully formed and understood, the shift toward a new global defense posture is beginning to accelerate.
Whenever the nation contemplates making a major shift in its global defense posture, planned changes should be seriously and broadly debated, because these changes will shape and constrain US strategic options for some time. In this regard, while the broad outlines for the ongoing shift in the US defense posture appear to be headed in the right direction, the changes have generally been made without much public or even internal governmental debate. Several important questions remain to be fully answered, and further changes will likely be required to address several existing or looming 21st century strategic challenges.