The fear that nations have of their rivals drives them to amass military strength, to which the rivals respond by redoubling their own security efforts ... and so on into the classic arms race that political scientists call the "security dilemma."
The Bush administration now tells us that our national objective is to solve the security dilemma by amassing so much power that no would-be competitor would even try to challenge us. Maybe this is possible; at least - as in "star wars"-like missile defense - nobody can be sure that it is not. Maybe it is even a good idea because, if successful, we will both end arms races and regain the position of seeming invulnerability that we enjoyed during much of our earlier history.
Moreover, our position of strength would give us a bully pulpit for transmitting our economic, political, and moral values and virtues - also a long-standing goal of Americans' foreign policy. As Americans are supposed to see it, Washington's benevolent and effective leadership would provide the world the long-desired prospect of peace and stability needed to promote growth and general happiness.
There are, however, several questions to be raised. Others have explored some of these - our continuing need for allies, for instance. But there are two other points that deserve attention.
The first asks an uncomfortable question for Americans: Are our values and virtues, as distinct from our affluence and popular culture, really universally admired and desired? And perhaps more to the point, despite President Bush's ritualistic affirmations of American goodness, would the world be a better place if our writ ran unchallenged?
Even while we take justifiable pride in the American role in helping to order the world after World War II, we know that we have made some terrible mistakes. We abhor the idea of even a benevolent dictatorship and, in our domestic politics, we recognize the importance of checks and balances as a bedrock of political organization. Is not the same true on a global basis? Might even we be better off in a world where we are occasionally challenged and called to account?
A second, more tangible issue is the reality that international society is organized around sovereign states. Individuals matter to some extent and international organizations sometimes play important international roles, but it is through nation states that individuals and most organizations pursue their interests on the world scene.
Under a new American empire, these states would have no effective way of standing up to the US, at least on political and security matters. Rather than engaging with governments with whom we can negotiate and whom we can, if necessary, bring to account, we would confront our opponents directly, as individuals and small groups.
We already see this in the Middle East, where the dominance of Israel is so great that there is hardly any conceivable Palestinian government that can stand up to Israeli pressure. The Palestinians, as individuals, and extra-governmental groups with behind-the-scenes support from the Palestinian Authority, have consequently turned to the weapon of the voiceless and powerless - terrorism.
This is a different kind of security dilemma, one that Israel has been unable to counter effectively and that is threatening that nation's very soul. Sept. 11 gave us in the US an early taste of it, and more is probably to come. There is no reason to assume that we will be more effective than the Israelis in devising a strategy to counter a terrorism that, in our case, would be world wide. In Harvard scholar Joseph Nye's image, we - like Rome - would risk being laid low not by a rival empire, but by countless minor wounds.
These are matters of supreme national importance and the administration is to be congratulated for putting its cards on the table. We can only hope that it is serious about engaging us in the kind of profound national debate that such questions deserve.
Before we set about reordering the world, we as citizens need to ask ourselves whether we have any realistic idea of what the costs and burdens will be. Lord Acton's dictum that power corrupts and absolute power corrupts absolutely should give us pause as we soberly consider whether even "the greatest nation in the world" should be entrusted - or even want to be entrusted - with such a task.
• Thomas P. Thornton is on the political science faculty of Johns Hopkins University. He previously held senior positions in the State Department and on the staff of the National Security Council.