Throughout history, as in many other parts of the world today, political rule was the privilege of the strongest or the most powerful. Property was the possession of kings, barons, and lords. Each was born to his or her destiny, and almost all were subject to someone else.

America is different because it is uniquely dedicated to the universal principles of human liberty: that all are fundamentally equal and equally endowed with unalienable rights to life, liberty, and the pursuit of happiness. Our government exists to secure these God-given rights, deriving its just powers from the consent of the governed. Our Constitution limits the power of government under the rule of law, creating a vigorous framework for expanding economic opportunity, protecting national independence, and securing liberty and justice for all.

In his Farewell Address, George Washington wrote that early United States foreign policy was designed “to gain time for our country to settle and mature its recent institutions, and to progress, without interruption, to that degree of strength and consistency, which is necessary to give it, humanly speaking, command of its own fortunes.” But then, as well as now, we could not command our fortunes in the world, protect national independence, and secure liberty without first providing for the nation’s security.

Safety and Happiness

Collective defense against external threats was the primary reason why the American colonies banded together in the first place. A key weakness of the Articles of Confederation was that it did not create sufficient capacity for security. By design, a chief purpose of the Constitution—and the particular obligation of the federal government—is to “provide for the common defence.” Congress and the President are given the power to provide for that defense, and the President, also commander in chief of the military forces, is both constitutionally and morally obligated to “preserve, protect, and defend the Constitution of the United States.”

In the Declaration of Independence, the right of the people to institute government means “laying its foundations on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness.” The pursuit of happiness is a natural right of liberty, but safety is the initial requirement of this pursuit. “Nations, as well as men, are taught by the law of nature, gracious in its precepts, to consider their happiness as the great end of their existence,” James Wilson wrote in his Lectures on Law. “But without existence there can be no happiness: the means, therefore, must be secured, in order to secure the end.”

In defending the new Constitution, Alexander Hamilton appealed in Federalist 43 “to the absolute necessity of the case; to the great principle of self-preservation; to the transcendent law of nature and of nature’s God, which declares that the safety and happiness of society are the objects at which all political institutions aim.” Necessity and self-preservation, the most basic requirements of safety, must be given their due before the higher claims of the happiness of society can be attended to.

It is the constitutional duty of the federal government to secure the country’s international borders and preserve and protect its territorial integrity, to strengthen and preserve its constitutional government, and to promote the long-term prosperity and well-being of its people. This means that the United States must be able, willing, and prepared at all times to defend itself, its people, and its institutions from conventional and unconventional threats to its vital interests, both at home and abroad.

The concept of national interest follows from the primary obligation to the community that constitutes the nation in the first place. “Under every form of government rulers are only trustees for the happiness and interest of their nation,” Hamilton wrote in the Pacificus essays, “and cannot, consistently with their trust, follow the suggestions of kindness or humanity toward others, to the prejudice of their constituents.” This is especially the case in a representative democracy in which the elected leaders have an obligation to act in the best interests of the people they represent and on whose behalf they exercise power. The first obligation of government is to the particular community it governs.

The requirements of security are dictated by the challenges and threats we face in the world. “How could a readiness for war in time of peace be safely prohibited, unless we could prohibit, in like manner, the preparations and establishments of every hostile nation?” asked Madison in Federalist 41.

The means of security can only be regulated by the means and the danger of attack. They will, in fact, be ever determined by these rules, and by no others…. If one nation maintains constantly a disciplined army, ready for the service of ambition or revenge, it obliges the most pacific nations who may be within the reach of its enterprises to take corresponding precautions.

The mission of the United States military is determined by America’s vital interests and an assessment of the threats to those interests. This should drive force structure requirements: how many brigades, wings, carrier groups, and other military assets are needed, where they are deployed, and how they are used. Force requirements and capabilities in service to the military’s overall strategic mission should determine the budget and spending needs for national defense.

The Common Defense Today

In recent years, despite unmatched rates of spending and government activity, the federal government has been doing less and less to fulfill its core responsibility of national defense.

Defense spending is near historical lows. Whether considered as a percentage of our economy or of the federal budget, the share that is spent by the Department of Defense is declining. General defense spending has fallen from 8.9 percent during the Vietnam War, 6 percent during the Reagan Administration, and 4.6 percent during the first Bush Administration. The budget for the core defense program in fiscal year (FY) 2011 was 3.7 percent. If the Administration’s current plans to cut defense succeed, that percentage will drop to 3 percent or lower.

By comparison, spending on Social Security, Medicare, and Medicaid has grown from 2.5 percent of GDP in 1965 to roughly 10 percent today—and these entitlements are projected to absorb all federal revenue by 2049. The President’s defense budget, even when coupled with the automatic defense spending cuts required by the 2011 Budget Control Act, will not solve America’s fiscal crisis. It will, however, drastically reduce America’s ability to deter aggression around the world.

Government spending, massive bloat, and constitutional overreach must be on the chopping block. But the core and undisputed constitutional responsibility of the United States government to provide for the common defense—especially at a time when we should be thinking seriously about our strategy and vital interests in an increasingly dangerous world—must not be up for negotiation.

Declining defense investments that force America to the margins of military superiority while countries like China and Russia invest heavily to modernize and expand their forces and rogue states like Iran and North Korea develop their nuclear weapons programs are risky and dangerous. To protect and defend America’s vital national interests, the U.S. military must have the tools it needs to deter attacks and enhance diplomatic efforts—and, when diplomacy and deterrence fail, to fight and win conflicts.

Be Prepared for War

American policy must not be driven either by the naïve notion that we can rid the world of tyranny and remake other nations in our image or by foolish claims that we can somehow withdraw from the world and isolate ourselves from threats to our sovereignty and independence. The better course—consistent with constitutional government, under which elected leaders have an obligation to act in the best interests of the people they represent and on whose behalf they exercise power—is to focus on America’s vital national interests in light of its principles, maintaining the United States’ freedom of action while prudently advancing liberty in the world.

President Washington liked to quote the old Roman maxim: “To be prepared for war is one of the most effectual means of promoting peace.” He was anxious that the country “leave nothing to the uncertainty of procuring a warlike apparatus at the moment of public danger.” Wise advice, indeed, that a free and independent country ought never to forget.

—Matthew Spalding, PhD, is Vice President, American Studies, and Director of the B. Kenneth Simon Center for Principles and Politics at The Heritage Foundation.