This being campaign season, our national foreign policy discussion is especially focused on the crises and conflicts taking place right now, with only the occasional glance backward at last season's failures and what we might learn from them. Russia intervenes in Syria, and we debate: Should we enforce a no-fly zone to assert our leadership? Or is it completely nuts to even talk about shooting down Russian warplanes to keep them out of a conflict that we, ourselves, ought to be steering clear of?

That sounds like a serious debate — and it is serious, in that the implications of getting the answer wrong could be disastrous. But relentlessly short-term and reactive thinking is hardly the most serious way to make policy in any area, much less in matters of war and peace.

If we want to think seriously about foreign policy for a change, we should start with the biggest-picture questions, the ones that are going to preoccupy us not only for the next news cycle or even the next year, but for the next generation.

Here's my top candidate: avoiding the Thucydides Trap.

The Thucydides Trap is named for the ancient historian of the Peloponnesian War, the long conflict between a rising Athens and Sparta and its allies that devastated the Greek world. Any time a new power rises rapidly, and seeks to revise the terms on which the previous international order is based, the dominant power risks falling into this trap. Today, the dominant power is America, and the rising power is China — and some, like Graham Allison, the director of the Belfer Center for Science and International Affairs at the Harvard Kennedy School, think the odds of a major war in the coming decades are quite high:

Based on the current trajectory, war between the United States and China in the decades ahead is not just possible, but much more likely than recognized at the moment. Indeed, judging by the historical record, war is more likely than not. Moreover, current underestimations and misapprehensions of the hazards inherent in the U.S.-China relationship contribute greatly to those hazards. A risk associated with Thucydides' Trap is that business as usual — not just an unexpected, extraordinary event — can trigger large-scale conflict. When a rising power is threatening to displace a ruling power, standard crises that would otherwise be contained, like the assassination of an archduke in 1914, can initiate a cascade of reactions that, in turn, produce outcomes none of the parties would otherwise have chosen. [The Atlantic]

The idea of war between China and the United States may seem absurd. Our two countries are mutual trading partners, and a major war would cause major economic harm to both countries. We have no substantial interests in conflict — China free-rides on the U.S. Navy's protection of the region's sea lanes, and China's territorial conflicts with its neighbors have little if any consequence for American security. Now that America is approaching energy independence, we should face markedly reduced causes for conflict over oil. And, finally, the catastrophic consequences of a nuclear exchange should make war unthinkable between any two countries with nuclear arsenals.

And yet, prior to World War I, Germany similarly benefited enormously from its trade with Britain, and from the naval Pax Brittanica. That didn't stop Germany from pursuing a naval arms race with Britain, and from pursuing its continental ambitions in a way that maximized the likelihood of conflict with Britain; nor did it stop Britain from making the containment and then the defeat of Germany its top foreign policy priority, one for which it mortgaged the future of, and then lost, its entire empire.

In an even more alarming precedent, Japan had a productive and friendly relationship with America for many years prior to the rise of Japanese militarism. Admiral Yamamoto, who led the attack on Pearl Harbor, had even studied in America, and understood just how powerful an enemy America would be. Yet Japan launched itself into war with America in 1941 despite an extremely poor prospect of success — because it saw no way for it to achieve its national ambitions without first removing America from the western Pacific.

Why is the Thucydides Trap called a trap? Because when faced with a rising, revisionist power, all courses of action can lead to war. A policy of accommodation can be readily interpreted as retreat, and invite aggressive expansion on the part of the rival. This, in turn, can create popular pressure in the dominant power for a reversal of policy — since that policy appears to be failing. On the other hand, a vigorous policy of containment can be readily interpreted as an attempt to encircle the rising rival, and provoke efforts to break out before the encirclement is complete. Moreover, the costs of maintaining hegemony steadily drain the resources of the dominant power, contributing to the rival's relative rise. All of these dynamics can be observed in the behavior of Britain and Germany in the run-up to World War I.

The two most notable cases where the dominant power avoided war were: Britain vis-a-vis the rise of America in the late-19th and early-20th centuries, and America vis-a-vis the Soviet Union during the Cold War. But Britain's accommodation of America began with the decision to respect the Monroe Doctrine, which cost Britain little, and ended with America dominating the planet and the British Empire relegated to the history books. And America's containment of the Soviet Union involved proxy wars all around the globe — and it's not clear that, after, say, 1950, the Soviet Union was in any meaningful sense a rising power relative to America.

Neither of those peaceful-endgame cases seems a very good model for dealing with the rise of China in an American-dominated world. America is unlikely to be willing to risk ceding total supremacy to the Chinese as Britain ultimately did to America — and Britain only did so because it had no choice when faced with the threat from Hitler. (Britain also had a close cultural affinity with America — but it's worth noting that, at the start of the 20th century, Anglo-German cultural affinity was arguably just as strong. In any event, no similar tie is likely to smooth understanding between America and China.) As for the Soviet comparison, China is a far more dynamic and powerful rival than the Soviet Union ever was, with a vastly larger industrial base and population. It has far more to offer in any contest for allies.

The way out of the Thucydides Trap, in Allison's view, is constant communication and a willingness to think very big in terms of accommodation. Americans should be prepared for a transition to a world in which China is not merely welcomed into the club of major powers, but is accepted as an architect of whatever world order is going to emerge. That level of accommodation is almost as impossible to imagine as is a major war between America and China. Which is precisely the reason to worry that we might be falling into the trap.

So it behooves us to take this question seriously — which means thinking very long-term, and with an openness to very large changes in the current international order. As well, it behooves us to always think about strategy elsewhere in the world, and how we repair the tattered institutions of collective security, in terms of how our choices affect this most important question.

But we're unlikely to debate those kinds of long-term questions any time soon. After all, it's campaign season.

Editor's note: An earlier version of this article stated that the U.S. is a net-exporter of oil. While the U.S. in recent years has been a net-exporter of petroleum products, this status been occasional rather than continuous. We regret the error.