NOW THAT EVERYONE AGREES we are at "war," it is time to think seriously about what that means.

The usual voices—from the European Union and its various agents of influence in America—warn us about the importance of "international cooperation." Americans who are eager to fight back may be tempted, on the other hand, to dismiss all talk about the rights of sovereign states. But now, more than ever, clear thinking about sovereignty is vital.

The first point to grasp is that, if we take words seriously, there is no such thing as "war" against abstractions like "terror"—or "drugs" or "poverty." War is a relation between sovereign states. The rest is merely policing—or empty rhetoric.

When armed men are shooting back, of course, "policing" may have little to do with lawyerly notions of due process. It can involve any force required to abate the violence.

Can we police outside our borders? In the classical conceptions of international law, sovereign states can deny outside powers the right to interfere in their own territory: That’s what sovereignty means. But this privilege comes with a price. A sovereign state is obligated to ensure that its territory is not used as a launching pad for attacks on the territory of other states. If the host state won’t take action, the victim state is entitled to do so.

This is not a doctrine invented in recent times by a starry-eyed U.N. conference. It follows from the basic idea of sovereignty. One state can only be expected to respect the territorial integrity of another when it is safe for it to do so.

So, for example, in 1842, British forces entered American territory from Canada to seize and destroy a ship loaded with arms for anti-British rebels in Canada. One American was killed in the resulting scuffle. Secretary of State Daniel Webster protested that the British action was precipitate. But he did not deny the principle that a state is authorized to protect itself when a neighboring state fails to repress such threats from across the border. Shortly after our Civil War, Irish nationalists tried to strike at the British Empire by launching a raid into Canada from American territory. The United States promptly apologized, cooperated in rounding up Fenians in New York, and offered compensation to Britain.

The principle remains very sound. When a state fails to suppress international terrorist networks, operating on its own territory, it is answerable to the countries targeted by the terrorists. A victim state is then justified when it acts in self-defense against the host state, even if the host state has indulged terror networks by negligence or fear rather than deliberate malice. There can be reasonable dispute about the timing and degree of defensive action, but not about the principle.

In planning our responses, we should not expect a great deal of military assistance from Europe or perhaps from many other countries. But we should certainly strive to get as much cooperation from other countries as we can. At minimum, we will need a lot of cooperation in gathering intelligence and closing escape routes for terrorist networks. That means it is much in our interest to keep the focus on terrorism—that is, on basic security—and not let ourselves get distracted by pompous rhetoric about democracy, liberty, or human rights.

China and Pakistan, for example, may prove valuable partners in some of our efforts. They have reasons of their own to be fearful of Islamist extremism and international terror networks. They cannot be expected to join a campaign for democracy, however, and it is no credit to democracy to enlist China and Pakistan under its banner. Right now it is our business to fight international terrorism, not any and all things of which we may disapprove. In the campaign against terrorism, pledging respect for the national sovereignty of our partners can be an asset and should not be seen as a reluctant concession.

When we do take military action, however, we must judge for ourselves the appropriateness of our measures. One thing we must therefore ask of our "allies" in Europe is that they at least put aside their fantasies of an international criminal court which would judge the legality of American actions.

This sort of thing is more than a distraction. It is a challenge to our own national rights. No international court can protect us against outside attack. No international court has any means to seize terrorists or to force harboring states to surrender them. Now that we have been attacked, no international court should presume to judge how we react in defending ourselves. If Europeans want to be neutral in the coming war, they should at least be told to respect the classic duty of neutrals—which is to refrain from judging the belligerents.

To those who regard all this as anachronistic, we should be more forthright. The terror menace has reached the scale it now has because too many countries—including our own—have been too willing to replace the historic claims of sovereign states with ineffectual and hypocritical international "understandings."

So the Palestinian Authority, which is not recognized as a sovereign state (and does not even claim to be one), is allowed to send delegates to international forums as if it were. Israel is told that it cannot interfere in "Palestinian territory," but the Palestinian Authority is not responsible for terrorist actions launched from that territory.

What is true for "Palestine" is true, in greater or lesser degree, for Syria, Libya, Iraq, and other sponsors of terror. We do not hold them to the standard of sovereign states. We have allowed them to connive with international terror, so long as they keep it below a certain acceptable level—and target it away from Europe or North America. Now it may be that states that have sponsored terror at a deniable distance have lost control of the most fanatic terrorist cells.

But the principle remains: If states do not suppress international terrorist operations on their own territory, they are failing in their most basic obligations. The victims of this failure are entitled to take up necessary policing duties on their own. Or they are entitled to regard host state failings as justification for war—against the sponsoring or negligent states. The United States now stands in the front rank of the victim states. And in war, toppling the other side’s government is a time-honored tactic. Let this be clear.

We may not replace the dictatorships of Saddam Hussein or Bashar al-Assad with a western-style democracy. But we can hope to see them replaced with regimes that know the price of their independence is reliable cooperation in suppressing terror attacks on outsiders. That is the duty of sovereign states. That’s what we should be fighting for. It is more than enough.


Jeremy Rabkin teaches international law at Cornell University.