We must also realize that it is impractical and likely impossible for us to destroy international terrorism networks alone. We must therefore cultivate support and seek assistance wherever we can, working closely with our allies abroad. Our aims will be most successfully accomplished if nations choose to drive out terrorism from their own land, and our most strenuous diplomacy should be employed in encouraging them to do so. But if we possess clear and irrefutable evidence, in our best judgment and in that of our allies, that a nation is sheltering those who have planned the terrorist attacks and who are now planning others, the use of allied military force is justified if necessary to protect U.S. soil.

The battle against terrorism may begin with the villains who brought down the World Trade Center and crippled the Pentagon, but it must not end there. Others would gladly appear to replace them, and the citizens of peaceful countries would feel no more secure. As so many world leaders have noted, this week’s attack was not merely an act of aggression against the United States, but against the free world. Once again, the duty to defend these freedoms has fallen squarely on our shoulders.