"First of all, it's evident that America is still today the world's foremost leader, partner, and underwriter of stability and security in every region across the globe, as we have been since the end of World War II. As we fulfill this enduring role, it's also evident that we're entering a new strategic era. Context is important here. A few years ago, following over a decade when we were focused on large-scale counterinsurgency operations in Iraq and Afghanistan, DoD began embarking on a major strategy shift to sustain our lead in full-spectrum warfighting. While the basic elements of our resulting defense strategy remain valid, it's also been abundantly clear to me over the last year that the world has not stood still since then-the emergence of ISIL [Islamic State of Iraq and the Levant], and the resurgence of Russia, being just the most prominent examples. This is reflective of a broader strategic transition underway, not unlike those we've seen in history following major wars. Today's security environment is dramatically different-and more diverse and complex in the scope of its challenges-than the one we've been engaged with for the last 25 years, and it requires new ways of thinking and new ways of acting."
U.S. Department of Defense: http://www.defense.gov/