National Defense Strategy: 2008
http://www.defenselink.mil/news/2008%20National%20Defense%20Strategy.pdf
Replaces the document released in 2005. Serves as a companion to the 2006 National Security Strategy. Sees the main threat to U.S. security in violent extremist ideologies like Al-Qaeda that seek to overturn the international state system. Also warns about rogue states like North Korea and Iran and challenges from China and Russia. From the Department of Defense