For the Founding Fathers, a primary and central duty of the federal government created by the Constitution is to “provide for the common defence.” The reason is simple: If we are not secure, we cannot be free.

As long as Americans value independence and liberty, the U.S. will need powerful armed forces to deter and defeat its enemies. But what we have to do to stay secure changes over time. A hundred years ago, we did not need an air force. Today we do. We know we need to provide for the common defense. But how should we do it now?

The United States is an exceptional nation because it is founded on universal truths. But it is also exceptional for a more commonplace reason. Around the world, most nations that have democratic governments are rich—but they are also small. The state of Colorado, for example, is larger than Britain. On the other hand, most nations that are very large are poor and not truly democratic—Russia, for example.

The United States is the one nation in the history of the world that is democratic, large, and rich. That is why America is the most powerful nation in history, and the world’s only superpower. We can protect our security, support our allies, and defend our interests around the world because we have the will to do it and the resources to afford it.

Of course, this works both ways. We could not have grown rich if we were not secure. The Founders recognized this and so they founded West Point and the U.S. Navy. Today, the same truth endures: If we are not secure, our economy will suffer. And if our economy stagnates, we will not be able to afford security.

So when you think about American security, the first thing you need to remember is that, in the long run, the strength of America rests not solely on its armed forces. It also rests in the growth, the energy, and the flexibility of the American economy. We need armed strength today to protect that economy, so that our children will be better off than we are today, and so they can in turn buy security for their children.

Today, the foundation of American security faces two fundamental challenges. First, our $16 trillion in national debt is rising quickly, but our economy is growing slowly. And we are doing many things that will make it grow even more slowly in the decades to come. Our government is spending more, borrowing more, taxing more, and regulating more. That will make it harder for people to find jobs, for entrepreneurs to start businesses, and for industry to expand.

The government is spending a greater share of its budget on welfare, old age, and other “entitlement” programs. And that is the second problem: Defense spending is being crowded out by this spending. If we do nothing, the problem will only get worse. Since most welfare and entitlement programs are on autopilot, they will continue to grow until we can afford nothing else.

Today, defense is already being squeezed badly. In a decade, the situation will be worse. Within two generations, the entire federal budget will be consumed by welfare and entitlement spending. There will be no money for anything else, including defense. All Americans have an obligation to their children not to let this happen. Understanding American security today means supporting policies that promote growth and restrain the rising cost of the welfare state.

But we can’t just buy defense when times are good. Defense is like an insurance policy. If you have to take a job that pays less, you should spend less on vacations and nice restaurants. But it wouldn’t be a good idea to stop paying your car insurance bill. Insurance protects you from big expenses that you can’t afford. When times are tight, you need insurance more, not less.

Right now, times are tight. But we still need to keep on paying the bill on our security policy. That means continuing to invest in defense research and development. It means buying the equipment that our soldiers, sailors, airmen, and marines need to do their job today, and compensating them fairly for doing it. And it means keeping a force that is large enough to defend our interests around the world. We need that force because Americans trade widely, travel widely, teach widely, and help widely. If we do not have defenses with a worldwide reach, it is not simply foreigners who will suffer: it will be our fellow Americans who travel and trade.

Today, a gap is opening up between the promises we have made to ourselves and to our allies and the reality of our armed forces. Our Army is losing entire brigades, the Navy is the smallest it’s been since 1917, and many planes in the Air Force are older than the pilots flying them. The defense budget is shrinking, spending on modernization is declining, and a wide range of vital programs—from the F-35 fighter jet to missile defense systems—are under threat of being cut.

Everyone agrees that defense spending should be efficient. But the quest for efficiency should not be used as an excuse to cut spending. If we cut now, we will sooner or later find ourselves with such a mountain of need to climb that it will be all but impossible to catch up.

Defense spending should not be a yo-yo that we yank up and down depending on what administration is in office or how the economy is doing. Understanding American security today means agreeing that we should spend a predictable and adequate share of our nation’s budget on defense.

The world is a dangerous place. It is impossible to be certain about the threats the United States will face, though we can make educated guesses. Many of today’s threats stem from international terrorism, the spread of nuclear weapons and other weapons of mass destruction, the rise of new powers, and the Internet.

International terrorism continues to threaten the United States. Since 9/11, we have foiled over 50 terrorist plots against us. The attacks of 9/11 were launched from faraway places, including Afghanistan. We have been fighting a war there so that it will not go back to being a haven for terrorists who would bring their war to our shores. We should never forget how we suffered that day, when America was under attack.

North Korea has successfully tested nuclear weapons and has launched missiles that can reach Hawaii. Iran aided terrorists in Iraq who murdered U.S. soldiers, and it is trying to build a nuclear weapon. If Iran succeeds, it will start a nuclear arms race in the Middle East and endanger our economy, our allies, and our bases in Europe.

In Russia, the future is bleak. Corruption is everywhere, and the hope of democracy is fading. President Vladimir Putin has made clear his plans to invest heavily in Russia’s military. In 2008, the Russian invasion of the Republic of Georgia, a democratic country and a friend of the United States, caught us by surprise and proved that Russia is willing to attack our allies for its own selfish reasons.

While Russia is on the decline, China is on the rise. We do not need to be paranoid about China: If we have foolish economic policies, we will hurt ourselves much more than China can. We need to remember that one of the purposes of the American armed forces is to discourage others from challenging us. In the Pacific we need to stay strong, not to fight a war but to ensure a war does not happen.

Finally, cyber warfare—war conducted over the Internet—is a reality. It is not something that “might” occur in the future. Cyber attacks on U.S. banks, our government, and our military are becoming more frequent and serious. Understanding American security today means recognizing that we need to have a military that can cope with all of these threats, as well as the ones we do not see coming.

Being prepared for this dangerous world means we have to keep our military ready to defend our interests. It also means that we have to follow economic policies that will allow us to pay for the kind of military we need. Understanding American security today means responding to the threats of today by applying the same principles we used to defeat the threats of yesterday. It means recognizing that George Washington was right to say, in his first State of the Union Address, that “To be prepared for war is one of the most effective means of preserving peace.”