The twenty-first century has brought new challenges to the world order. Climate change may be the most disruptive in the long run but new forms of pandemic illness may be a chronic threat now. These dangers may worsen as a result of overcrowding in habitable places.
But a more traditional kind of challenge has also returned, a world of traditional great power rivalry. Adding to this threat will be the continuing spread of dangerous technologies, as modernizing nations narrow the technical gap separating them from more advanced nations. Some of these technologies may come within reach of private groups.
Ending great power rivalry is the key to meeting other dangers. This rivalry will continue as long as national interests supersede global ones. However, rivalries tend to end, at least for a time, when one great power (or group of powers) is unable to sustain the rivalry. These moments are rare and usually result in the prevailing power achieving dominance. But unless this power is able to rule indefinitely, such dominance is likely to end as it has for dominant great powers in the past.
An alternative is for a prevailing great power to form alliances with former great power adversaries. This can only work if three conditions can be met: all of the great powers have compatible regimes, all respect the sovereignty of smaller nations, and all embrace peaceful cooperation. An alliance cannot work if defeated powers harbor ambitions of revenge. But a desire for revenge may be greatly lessened by the degree of inclusion in the world order that follows the moment when previous rivalry ends.
The United States has been the dominant maritime power since 1945 and the leading power in Europe since 1991. The era of this dominance is probably ending now as rival powers such as Russia and China move to dominate their respective regions. The result is likely to be war between America and China if the former rearms to meet the growing armaments of the latter. Russia and the rest of Europe are likely to be drawn into such a conflict.
The outcome of current and future tension is not possible to know in advance. If America's adversaries prevail, then they will dictate the terms of peace. But the United States can do more than arm itself for a confrontation. It can also plan for an aftermath in which its adversaries do not prevail. This aftermath could differ from what happened after the Cold War ended in 1991. This time, America could offer alliances to Russia and China, subject to the three conditions above. Alliances have rarely endured and may fail again. But not to attempt cooperation on a new basis, if former adversaries undergo changes in regime and policy, will guarantee that the world order remains largely unchanged. Longer-term dangers will then be more difficult to overcome.