Terrorists have attacked our people, our economy and our way of life. They hope to undermine not only our confidence in ourselves, but also the confidence of the world in us. Above all, they want to test our resolve. The terrorists will have succeeded if, because of confusion or self-imposed constraints, we forget what happened yesterday and go on in a few weeks time as if nothing fundamentally has changed. Something fundamentally has changed and we have to begin acting on that basis.

This is not the first time Americans have been attacked or even killed by terrorists. Repeatedly, each time Americans were attacked and in some cases killed, the initial shock wore off, and slowly but surely we got back to business as usual. When hundreds of Marines were killed in Beirut by terrorists in the 1980s, we were shocked. But slowly we forgot about it and got back to business as usual. When people associated with known terrorist Osama Bin Laden attacked the World Trade Center in the early 1990s, we were outraged, but soon we forgot about that too. When other terrorists suspected of being associated with Bin Laden attacked U.S. troops in barracks in Saudi Arabia, and even U.S. sailors on the U.S.S. Cole in port at Yemen, we were outraged. But we then we soon forgot that as well. When our embassy personnel in Kenya and Tanzania were attacked by terrorists and hundreds of people were killed (again by people associated with Bin Laden), we were shocked, but again we forgot. Each time Americans were targeted and in some cases hundreds were killed, but each time we let down our guard, and made it possible for them to attack again.

Will we forget this time as well? Will we let our guard down again? Will we ignore the warnings and sink once again into the complacency that made us vulnerable to the most deadly foreign attack on U.S. soil ever (yesterday we undoubtedly lost more Americans in a single day than we lost in the entire War of 1812, and we lost more than at Pearl Harbor).

This time it must be different. We cannot go back to business as usual.

While yesterday's attack was a crime against humanity, it was above all an act of war directed against the United States. Therefore, the United States' response must be, out of self-defense, a systemic and comprehensive war against all forms of international terrorism.  We should not treat this horrible act as a mere crime that must end up in some international court of justice. Neither should we establish inappropriately high standards of proof better suited for the courtroom than for a field of battle. Rather, we should treat these attacks as acts of war that require strong and resolute measures of self-defense.

To avoid the possible return of complacency, the President and the Congress must act quickly to ensure specific measures are taken soon to mobilize the nation to meet the various threats that exist to the nation, including terrorism.

This means, first and foremost, that the President should ask Congress for a declaration of war against any international group and/or state that participated in yesterday's attack. This would make America's resolve clear, and eliminate any confusion about the methods needed to solve the problem. Responding to yesterday's attack should be the job of the U.S. military, intelligence and security forces to handle; not the job of the United Nations, lawyers or international courts. The military response must be effective and decisive, and not be seen merely as sending signals or even as retribution per se. We want to solve the problem, not merely express our outrage or anger with symbolic gestures. We need to root out the networks that support terrorists, and not just retaliate against individuals.

This means finding hidden enemies who are waging war against us and destroying them completely, their supporters, and the infrastructure that enabled them to attack us.

It means holding accountable the states that harbored or supported these terrorists in any way.  If a regime is found to have harbored or supported these terrorists, it should be the goal of U.S. policy to remove that regime from power with any means necessary. The means to be used should be decided by the President and the Secretary of Defense, with consultations with Congress, but as much leeway as possible must be given to the military commanders for deciding the exact methods to be used. As for other states that may have indirectly supported the terrorists, the U.S. should use whatever means are necessary to punish them, or to force a change in their policies.

It means demanding support not merely from allies but from other countries that wish to be known as civilized states. This includes not only Russia and China, but also Arab states that depend on the U.S. for their security, and which have not been as cooperative as they should be in destroying our common enemy. There should be complete and close international cooperation to root out these terrorist organizations no matter where they are.

This means the Congress must give the President whatever he asks for by way of funding for military and security operations, intelligence assets, and building up our armed forces to meet the palpable threats that have for too long been discounted and in some cases even ignored.

This means beefing up our intelligence capabilities, which have been sorely neglected in recent years, in terms of working with sometimes unsavory characters who can help us, of vastly improving our technical capabilities to monitor terrorist activities, and of providing better analysis of what we can find out.

It means that we have to get very serious about providing better security at our airports, which has been woefully lacking. This will require Americans to be more patient about security methods and to be more understanding of the sometimes unpleasant but necessary methods used to provide airport and other infrastructure security. It will also require better guidance from the U.S. government on how to provide airport security.

It means that we must have a comprehensive homeland defense policy that defends the American homeland not merely against such terrorist attacks that occurred yesterday, but against other ones and new ones that are emerging-such as attacks on our computer infrastructure; on our financial systems; and on our communications, transportation, water and fuel network and supplies.

Finally, we must end our complacency about the missile threat and start building a defense against ballistic missiles, which inevitably will be the next weapon of choice for terrorist states. There are 20 nations that are either developing or deploying ballistic missiles. They include such rogue states as North Korea, Iraq and Iran. Why do we suppose that when they get the capability to rain death down on millions of Americans with a missile, that they would not choose a method that is so easy and devastating as a missile attack?

It does no good to argue that no defenses against missiles are needed because terrorists found other means, like yesterday's hijacking of U.S. commercial airlines, to attack Americans. We must defend ourselves not only against current types of terrorism but against future types that will inevitably involve nuclear, chemical and biological weapons placed on ballistic missiles. It is not a question of either/or, but of defending against both missiles and other means of terrorist attacks.

We have received yet another warning. The next threat will be from some weapon of mass destruction-a nuclear, chemical or biological devise-that may either be placed on a missile, an airplane, boat or some other means of delivery. We must be prepared to defend against all of these threats. We must hope that the complacency and self-delusion that made yesterday's attack possible does not return to prevent us, once again, from defending ourselves against the rising threat of missiles, nuclear arms, and chemical and biological agents.

Kim R. Holmes, Ph.D. is Vice President of Foreign and Defense Policy Studies and Director of the Kathryn and Shelby Cullom Davis Institute for International Studies at The Heritage Foundation.