During the latter half of the 20th century, U.S. defense efforts were driven by the need to respond to the threat posed by the Soviet Union. While the Soviet threat was considerable, the U.S. response was facilitated by the focus on a single adversary. The current situation is quite different. Today, the U.S. faces a disturbingly diverse set of national security challenges ranging from Somali pirates to transnational terrorist organizations to rogue nations with nuclear weapons. In the 21st century, the only viable approach to national security is to maintain an adequately sized, trained, and equipped force that is capable of dissuading, deterring and—if necessary—defeating a diverse set of future adversaries.

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