A shift in the international security environment could have significant implications for U.S. defense plans and programs. A previous shift in the international security environment--from the Cold War to the post-Cold War era--prompted a broad reassessment by the Department of Defense (DOD) and Congress of defense funding levels, strategy, and missions that led to numerous changes in DOD plans and programs. The issue for Congress is whether a shift in the international security environment has occurred, and if so, how to respond to that shift. This report briefly describes the shift in the international security environment that some observers believe has occurred, and identifies some defense-related issues for Congress that could arise from it. Congress' decisions on these issues could have significant implications for U.S. defense capabilities and funding requirements.