A new kind of empire?

Two hundred years and a few weeks ago, William C.C. Claiborne, governor of the Mississippi Territory, and Gen. James Wilkinson arrived in New Orleans and formally accepted transfer of the province of Louisiana from the French to the United States.

Overnight, the Louisiana Purchase doubled the nation's land mass. And it offered the first real fuel to American expansionism. The infant nation would go on to become a continental power, a world power, and eventually a superpower. With increasing confidence, it manufactured its goods, built up its military, and exported its ideas. Now, it has reached a pinnacle of power that would be the envy of any empire before it.

Its military superiority and reach far outclass what Rome achieved in its day (see below). Its economic influence, while somewhat diminished from its postwar heights, remains dominant (see page 16). And its cultural exports reach every corner of the globe with unprecedented speed (see page 17).

But if America qualifies as an empire, it's a nontraditional one. Its overseas territories are paltry: 14 dependencies, mostly tiny Pacific islands, and no apparent appetite for more land. It backs an economic system that has allowed some trade partners to outcompete it. In the past, its invasions have been followed by departures, although often leaving behind governments friendly to its political and economic interests.

But the war on terror is changing that equation. By claiming the right to strike preemptively, the US is raising alarms in many world capitals. Demonstrating its willingness to effect regime change unilaterally, Uncle Sam is flexing his muscle as never before.

Depending on one's outlook, the result could be a safer world. Or the first steps along a dangerous path.