American decline and the longevity of a unipolar world order will not be determined purely by economic gains or losses. The future shape of the international system will depend on broader measures of national power than the percentage of global production that a given state controls. Measuring national power, however, is notoriously difficult. In an unprecedented situation of unipolarity, with little historical precedent to guide analysts, the measurement of relative power shifts is perhaps harder still.
The main metrics tend to include GDP, population, defense spending, and then a variety of other factors. There are differences among the various methods as to how one might quantify or otherwise measure many of the factors. But since all agree that these kinds of measurements are inherently subjective it is not surprising that slightly different factors and different weights to different factors can lead to differing results. It is not clear how much these models can account for discontinuities and dynamic changes as opposed to straight-line projections and relative shifts in power. Nor is it clear that the models can really measure the all-important question of how world leaders perceive shifts in relative national strength and power. The key factor would seem to be getting at the ability of countries to convert resources into usable power combining both hard power and soft power.
At the end of the day, at least as important as the objective measures of national power are the subjective assessments of international statesmen and military leaders about the international distribution of power. Those judgments are inevitably affected by a range of cultural, psychological, bureaucratic and political factors. The debate over American decline and whether or not we are entering a multipolar, as opposed to unipolar, world in and of itself will inevitably have an impact on those subjective judgments.
Our assessment of putative powers, however, will cover the traditional contenders, Europe and Japan, and include the so-called BRICs as well.
Europe
Many of the declinist predictions of the late 1990s, as well as the most recent wave, have taken as a point of departure that a united Europe will comprise a key component of a prospective multipolar world. Even before the economic crisis began to take the wind out of European sails, the EU was not effectively translating its economic potential into power on the international stage. The persistence of national differences (and sensitivities) on foreign affairs have contributed to the failure to develop a “common strategic culture.”
Continued dependence on the United States security guarantee has allowed Europeans to spend less for their own security. These considerations have forced even Euro-triumphalists (who otherwise believe that America is in decline, the United States must adjust its policies, and Europe must become part of the “post-American world”) to admit that Europe maintains a set of shared interests with the US, relies on US security guarantees and a series of “special relationships” to maintain stability.
Europe’s biggest challenge is demographic. It is a challenge that has the potential to exacerbate both economic and social problems in Europe and renders even more unlikely the notion that Europe will increase its military power or be willing to wield it outside of Europe. Even if Europe were able to surmount these demographic trends, the political challenges of deeper and more extensive European integration remain. As Global Trends 2025 suggests the EU could well become a “hobbled giant distracted by internal bickering and competing national agendas, and less able to translate its economic clout into global influence.”