He explains why in an article posted at National Review:

As we enter this new decade, we are being lectured that China is soon to be the global colossus. Its economy is now second only to America?s, but with a far faster rate of growth and with budget surpluses rather than debt. Few seem to mention that China?s mounting social tensions, mercantilism, environmental degradation, and state bosses belong more to a 19th- than a 21st-century nation.

Amid all this doom and gloom, two factors are constant over the decades. First, America goes through periodic bouts of neurotic self-doubt, only to wake up and snap out of it. Indeed, indebted Americans are already bracing for fiscal restraint and parsimony as an antidote to past profligacy.

Second, decline is relative and does not occur in a vacuum. As Western economic and scientific values ripple out from Europe and the United States, it is understandable that developing countries like China, India, and Brazil can catapult right into the 21st century. But that said, national strength is still measured by the underlying hardiness of the patient ? its demography, culture, and institutions ? rather than by occasional symptoms of ill health.

In that regard, America integrates immigrants and assimilates races and ethnicities in a way Europe cannot. Russia, China, and Japan are simply not culturally equipped to deal with millions who do not look Slavic, Chinese, or Japanese. The Islamic world cannot ensure religious parity to Christians, Jews, or Hindus ? or political equality to women.

The American Constitution has been tested over 223 years. In contrast, China, the European Union, India, Japan, Russia, and South Korea have constitutional pedigrees of not much more than 60 years. The last time Americans killed each other in large numbers was nearly a century and a half ago; most of our rivals have seen millions of their own destroyed in civil strife and internecine warring just this past century.