U.S. Power in the 21st Century

The United States was the most powerful country in the world throughout the 20th century.

There was talk in the late 1980s that the United States had reached the apogee of its power and was likely to decline in the years ahead — much the way Britain's strength withered away after 1900.

But that pessimism was short-lived. By the mid-1990s — with the Soviet Union gone and the U.S. economy catching fire — it became fashionable to call the United States a global hegemon.

But what does America's trajectory look like now?

Instead of declining, it looks like the United States will become even more powerful in the 21st century than it was in the 20th century.

Power in the international system is largely a function of two factors: population size and wealth. Great powers are invariably the states with the largest populations and the most wealth.

Population size matters because great powers require large militaries and because only large populations can produce abundant wealth.

Wealth is important because a state cannot build a powerful military if it does not have the money and the technology to equip, train and continually modernize its fighting forces.

Furthermore, the costs of waging war are enormous, as we are now discovering in Iraq. Although the U.S. military easily routed Saddam's army, the war and the occupation have already cost us about $150 billion.

Imagine the cost of engaging a formidable adversary, not a feeble one like Iraq. In short, the mightiest states in the world have to be both populous and rich.

The main reason to think that the United States will grow increasingly powerful over time is demography. America's population is likely to grow at a rapid clip over the next 50 years, while its potential rivals are likely either to shrink or grow modestly.

Consider Germany, Japan and Russia — our three main rivals during the past century.

The United Nations projects that Germany's population, which was 82 million in 2000, will shrink to 79 million in 2050.

Japan's population, which was 127 million in 2000, is projected to shrink to 110 million in 2050.

Finally, the UN expects Russia's population, which was 146 million in 2000, to shrink to 101 million in 2050.

If these projections prove accurate, Germany's population will shrink by 4%, Japan's by 13% — and Russia's by 31%.

What about Britain and France? Their populations are both likely to grow, but not much.

Britain had 59 million people in 2000 and is expected to grow to 66 million in 2050. France — which also had 59 million people in 2000 — is projected to reach 64 million in 2050.

The British and French populations, in other words, are expected to grow by 12% and 8%, respectively, over the next 50 years.

Contrast these projections with the expected numbers for the United States.

There were 285 million Americans in 2000. The United Nations predicts that our population will grow to 409 million by 2050 — an increase of 44%.

Some experts believe that the American population will be 500 million by 2050, which — if proved correct — would represent a staggering 75% increase in size.

What about China? For sure, China is the one country that might someday challenge the United States. It certainly has a huge population.

The UN estimates that there were almost 1.28 billion Chinese in 2000 and that their numbers are likely to grow to about 1.4 billion by 2050, which is a modest 9% growth.

Moreover, China has experienced robust economic growth over the past 25 years — and there is no sign that its economy is running out of steam.

Nevertheless, there is reason to doubt that China will emerge as a serious threat to the United States.

Because of China's one child policy, its population is aging at a rapid pace, which is likely to act as a drag on its economy over time.

Not only does China have an inadequate pension system, but it will be increasingly difficult for its work force to support its vast army of retirees, mainly because the number of workers per retiree will decrease sharply over time. Moreover, most retirees will have only one child to whom they can turn for support.

But China is not the only country with a graying population. Japan is aging even more rapidly.

In fact, almost all of the advanced industrial countries are facing serious problems on this front, except for the United States — which will remain relatively youthful in the years ahead, and thus avoid the economic problems that come with a surfeit of senior citizens.

There is another reason why the American economy is likely to remain dynamic.

One of the essential ingredients that societies need to generate wealth is a large pool of smart and ambitious people.

The United States not only has an abundance of homegrown talent, but it also acts like a giant vacuum cleaner sucking up talented foreigners from all corners of the globe and transforming them into American citizens.

The University of Chicago, I might add, plays an important role in making that aspect of the melting pot work well.

Other industrialized countries, however, tend to be suspicious of — if not hostile to — foreigners, which puts them at a disadvantage relative to the United States.

The bottom line is that — with the possible exception of China — the United States is likely to be more powerful in the new century than it was in the last century, when it was the 800-pound gorilla on the block.

This essay was adapted from Mr. Mearsheimer’s speech at the University of Chicago’s 2004 commencement.