The change sweeping the Arab world has brought to the forefront a controversy dating to the early days of our Republic. Should American military might be used for idealistic reasons or as an expression of a vital national interest? Or both? Having served four U.S. presidents during a variety of international crises, we view the choice between “idealism” and “realism” as a false one. Just as ideals must be applied in concrete circumstances, realism requires context for our nation’s values to be meaningful. To separate them risks building policy on sand.

Like most Americans, we believe that the United States should always support democracy and human rights politically, economically and diplomatically, just as we championed freedom for the captive peoples of the Soviet empire during the Cold War. Our values impel us to alleviate human suffering. But as a general principle, our country should do so militarily only when a national interest is also at stake. Such an approach could properly be labeled “pragmatic idealism.”

Libya is arguably an exception to the rule. While the United States did not have a vital interest at stake in Libya, a limited military intervention solely on humanitarian grounds could be justified. Moammar Gaddafi’s forces had already caused heavy casualties among civilians and were on the verge of capturing Benghazi, with possibly dire consequences for its inhabitants. Gaddafi’s armed forces were weak. He was unpopular at home and friendless abroad. Both the U.N. Security Council and the Arab League had called for action.

Nevertheless, our idealistic goals cannot be the sole motivation for the use of force in U.S. foreign policy. We cannot be the world’s policeman. We cannot use military force to meet every humanitarian challenge that might arise. Where would we stop? Syria, Yemen, Algeria or Iran? What about countries that have been strong allies but do not share all of our values, such as Bahrain, Morocco and Saudi Arabia? What about humanitarian violations in other countries, such as Ivory Coast?

As events unfold in North Africa and the Middle East, it is imperative that we look at each country individually. In this spirit, we offer a few guidelines:

First, when using force, we must establish a clear and specific goal. The objective of protecting civilians is consistent with our values. But it is inherently difficult to keep such an effort limited. The need for humanitarian intervention almost invariably arises from the necessity of protecting populations from their own governments or from the collapse of government altogether. This provides incentives for strategic foreign policy considerations, such as regime change or nation building. But if we articulate a goal of regime change in conjunction with military intervention, we will be expected to employ the means required to effect it. A disconnect risks confusion among allies, adversaries and the American public, as well as mission creep. Failure to achieve proclaimed objectives then turns into a strategic setback.

Second, we should examine the circumstances in each country in terms of its specific conditions and seek to relate its culture and history to our strategic and economic interests. This will allow us to analyze the motives behind the various mass demonstrations and develop appropriate individual responses to each.

Third, we must know exactly what and whom we are supporting. In Libya, we have in effect taken sides in a civil war. But it is not enough to oppose a despot. We need some assurance that a succession would not create its own major problems; therefore, it is important to have a concept of order after regime change. The last thing the region needs is a series of failed states.

Fourth, there must be domestic support in the United States, which is usually obtained by congressional backing. Conducting policy without such support is very difficult in the short term and unsustainable in the long term. The experiences of the Korean, Vietnam and second Iraq wars show that prolonged stalemates sap public support.

Fifth, we should consider unintended consequences. We need to think about how to protect pro-Gaddafi civilians from atrocities at the hands of rebel forces. The action in Libya may tempt the Iranian regime to speed its development of a nuclear weapon, especially when Iranians consider that Gaddafi gave up his nuclear program for closer ties to the West. Rogue states have to remain convinced of our determination to resist nuclear proliferation.

Sixth, and most important, the United States must develop a firm and differentiated understanding of its vital national interests. Not every upheaval in the region has the same origin or remedy. The Arab Spring has the potential to become a great opportunity for the people of the region and the world. Over time, fostering democracy may provide an alternative to Islamic extremism; it may also, in the short term, empower some of its supporters. We need to develop a realistic concept of what is achievable and in what time frame.

We have a vital interest in long-term stability in the Arabian/Persian Gulf, the source of much of the world’s energy. We have a similarly critical interest in seeing that countries in the region do not become breeding grounds for Islamic extremists.

The United States should pursue a policy that couples our determination to protect our national interests with promotion of the values that have made our country great — democracy, freedom and human rights. Such a policy of pragmatic idealism is the best way to confront the challenges and opportunities of the momentous transformation taking place in the Islamic world.

Henry A. Kissinger was secretary of state from 1973 to 1977. James A. Baker III was secretary of state from 1989 to 1992.