A core responsibility of the U.S. Government is to protect the American people - in the words of the framers of our Constitution, to "provide for the common defense." For more than 230 years, the U.S. Armed Forces have served as a bulwark of liberty, opportunity, and prosperity at home. Beyond our shores, America shoulders additional responsibilities on behalf of the world. For those struggling for a better life, there is and must be no stronger advocate than the United States. We remain a beacon of light for those in dark places, and for this reason we should remember that our actions and words signal the depth of our strength and resolve. For our friends and allies, as well as for our enemies and potential adversaries, our commitment to democratic values must be matched by our deeds. The spread of liberty both manifests our ideals and protects our interests. The United States, our allies, and our partners face a spectrum of challenges, including violent transnational extremist networks, hostile states armed with weapons of mass destruction, rising regional powers, emerging space and cyber threats, natural and pandemic disasters, and a growing competition for resources. The Department of Defense must respond to these challenges while anticipating and preparing for those of tomorrow. We must balance strategic risk across our responses, making the best use of the tools at hand within the U.S. Government and among our international partners. To succeed, we must harness and integrate all aspects of national power and work closely with a wide range of allies, friends and partners. We cannot prevail if we act alone. The President's 2006 National Security Strategy (NSS) describes an approach founded on two pillars: promoting freedom, justice, and human dignity by working to end tyranny, promote effective democracies, and extend prosperity; and confronting the challenges of our time by leading a growing community of democracies. It seeks to foster a world of well-governed states that can meet the needs of their citizens and conduct themselves responsibly in the international system. This approach represents the best way to provide enduring security for the American people. The National Defense Strategy (NDS) serves as the Department's capstone document in this long-term effort. The NDS describes our overarching goals and strategy. For the foreseeable future, this environment will be defined by a global struggle against a violent extremist ideology that seeks to overturn the international state system.