A world with no one in charge

As for Taiwan, China has 1,500 short-range ballistic missiles pointed at the island, even as hundreds of commercial flights each week link Taiwan with the mainland in peaceful commerce. When China effectively incorporates Taiwan in the years to come, that will signal the arrival of a truly multipolar and less predictable military environment in East Asia.

In the Middle East we see the real collapse of the Cold War imperial order. The neat Israeli-Arab dichotomy that mirrored the American-Soviet one has been replaced by a less stable power arrangement, with a zone of Iranian influence stretching from Lebanon to western Afghanistan, pitted against both Israel and the Sunni Arab world, and with a newly Islamic, and no longer pro-Western, Turkey rising as a balancing power.

Yes, empires impose order, but that order is not necessarily benevolent, as Iran's budding imperial domain shows. U.S. threats against Iran lack credibility precisely because of our imperial fatigue resulting from Iraq and Afghanistan. Out of self-interest we will probably not involve ourselves in another war in the Middle East - even as that very self-interest could consign the region to a nuclear standoff.

One standard narrative is that as we recede, China will step up as part of a benign post-American world. But this presupposes that all imperial powers are the same, even when history clearly demonstrates that they are not. Nor does one empire sequentially fill the gap left by another.

While the Soviet Union and the United States were both missionary powers motivated by ideals - communism and liberal democracy - through which they might order the world, China has no such grand conception. It is driven abroad by the hunger for natural resources (hydrocarbons, minerals and metals) that it requires to raise hundreds of millions of its citizens into the middle class.

This could abet the development of a trading system between the Indian Ocean, Africa and Central Asia that might maintain peace with minimal American involvement. But who is to fill the moral void? Does China really care if Tehran develops nuclear weapons, so long as it has access to Iran's natural gas? And Beijing may not be entirely comfortable with the North Korean regime, which keeps its population in a state of freeze-frame semi-starvation, but China props it up nevertheless.

It can be argued that with power comes moral responsibility, but it will probably be decades before China has the kind of navy and air force that would lead it to become an authentic partner in an international security system. For the moment, Beijing gets a free ride off the protection of the world's sea lanes that the U.S. Navy helps provide, and watches us struggle to stabilize Afghanistan and Pakistan so that China can one day extract their natural resources.

If the Cold War was an epoch of relative stability, guaranteed by a tacit understanding among empires, we now have one waning empire, that of the United States, trying to bring order amid a world of rising and sometimes hostile powers.

Looming over all of this is the densely crowded global map. Across Eurasia, rural populations have given way to megacities prone to incitement by mass media and to destruction by environmental catastrophe. Lumbering, hard-to-deploy armies are being replaced with overlapping ballistic missile ranges that demonstrate the delivery capabilities of weapons of mass destruction. New technologies make everything affect everything else at a faster and more lethal rate than ever before. The free flow of information, as the WikiLeaks scandal makes clear, and the miniaturization of weaponry, as the terrorist bombings in Pakistani cities make clear, work against the rise and sustenance of imperial orders.

The American empire has always been more structural than spiritual. Its network of alliances certainly resembles those of empires past, and the challenges facing its troops abroad are comparable to those of imperial forces of yore, though the American public, especially after the debacles in Iraq and Afghanistan, is in no mood for any more of the land-centric adventures that have been the stuff of imperialism since antiquity.

Americans rightly lack an imperial mentality. But lessening our engagement with the world would have devastating consequences for humanity. The disruptions we witness today are but a taste of what is to come should our country flinch from its international responsibilities.