One important question Allison’s book raises is whether the strongest states in the international order behave differently from other states. A hegemon is the rule setter and enforcer in the international order. It is typically (but not necessarily) the strongest power, because states fight for the right to establish terms favorable to their interests—so Britain after the Napoleonic Wars, which “ruled the waves,” could waive the rules; and the United States in the 20th century and especially after World War II became the architect of what is called the liberal international order, or the rules-based international order.

Parent and McDonald survey power transitions since 1870 (when data on gross domestic product first started being reliably collected) to explore the behavior of both the top states in the order and the lesser but still powerful states. They examine 16 cases of relative decline, some by hegemonic powers and some by mid-level states.

What they find is that most states respond sensibly to relative decline, undertaking prompt, proportionate retrenchment, because they seek strategic solvency—they don’t want to go bankrupt (and thus lose their independence). That is, the sensible policy choices that helped make them powerful also help them cope with straitened circumstances and decide to reduce their military and avoid armed conflicts. For most states, the choice of retrenchment helps them regain stature; those that fail to retrench never do.

The authors also find that states experiencing decline are not generally seen as inviting targets for aggression by others. So rising states are not generally tempted to attack a weakening rival. Parent and McDonald’s research suggests this is because the states experiencing decline steer clear of conflicts—war being the unsentimental arbiter of state power, declining states would rather not risk demonstrating their diminution. Their research also suggests that these states tend to prevail in the conflicts they do choose to initiate. Parent and McDonald conclude, “This suggests that declining powers are flexible and formidable.”

The Chinese Communist Party leadership would have benefited from Parent and McDonald’s research, showing as it does that “premature bids for hegemony can not only encourage the formation of hostile foreign coalitions but also upset the fragile domestic foundations of long-term growth.” For all the talk of China’s leaders as brilliant strategists with a hundred-year time horizon in their planning, their choices in the past decade would seem to conform to Parent and McDonald’s description of a premature bid for hegemony.

This is all good news for the United States in a time of waning relative power in the international order. If the future conforms to the data, we can expect a United States that gets its house in order while avoiding wars, as the Chinese activate antibodies against their continued rise, and thereby allow the U.S. to regain its former standing. This is not as good news for America’s allies, who will have to bear more of the cost, risk, and responsibility of defending their security and sustain an international order beneficial to their interests.