The United States is getting tagged as an "empire" from all quarters. Indeed, it's been a century since the notion of an American empire got such wide circulation, and back then Washington truly had designs on such expansion. (Google "Spanish-American War" if you're interested.)

The empire charge has long been a staple of the political extremes. It's even bubbled up in the presidential race. Lefty Rep. Dennis Kucinich insists that we must abandon "the ambitions of empire." Hyper-libertarian Rep. Ron Paul says we could afford health care if we weren't running a "world empire."

My problem is that the word "empire" usually substitutes for an argument; there are no good empires, just as there are no good fascists, or racists, or dictators.

In recent years, however, there's been an attempt to rehabilitate the e-word. Historian Niall Ferguson deserves primary credit for the mainstreaming of the empire debate with his 2004 book "Colossus." He faced the empire charge head-on, saying, in effect, "Yeah, so what's your point?" The world needs a stabilizing watchman to keep the bad guys in check and to promote trade, he argued, and America is the best candidate for the job.

Ferguson concedes that the American people don't want an empire, don't think that they have one, and that even our elites have no idea how to run one. As David Frum noted in the National Review, Ferguson "repeatedly complains that his particular fowl neither waddles nor quacks - and yet he insists it is nevertheless a duck."

Even as he strives to rehabilitate the idea of empire, Ferguson acknowledges the word's limitations. It "is irrevocably the language of a bygone age," he concludes. It's become irretrievably synonymous with villainy.

America's critics point out that the U.S. does many things that empires once did - police the seas, deploy militaries abroad, provide a lingua franca and a global currency - and then rest their case. But noting that X does many of the same things as Y does not mean that X and Y are the same thing. The police provide protection, and so does the Mafia. Orphanages raise children, but they aren't parents. If your wife cleans your home, tell her she's the maid because maids also clean homes. See how well that logic works.

When they speak of the American empire, critics fall back on cartoonish notions, invoking Hollywoodized versions of ancient Rome or mothballed Marxist caricatures of the British Raj. But unlike the Romans, or even the British, our garrisons can be ejected without firing a shot. We left the Philippines when asked. We may split from South Korea in the next few years under similar circumstances. Poland wants our military bases; Germany is grumpy about losing them. When Turkey, a U.S. ally and member of NATO, refused to let us invade Iraq from its territory, the U.S. government said "fine." We didn't invade Iraq for oil (all we needed to do to buy it was lift the embargo), and we've made it clear that we'll leave Iraq if the Iraqis ask.

The second verse of the anti-imperial lament, sung in unison by liberals and libertarians, goes like this: Expansion of the military-industrial complex leads to contraction of freedom at home. But historically, this is a hard sell. Women got the vote largely thanks to World War I. President Truman, that consummate Cold Warrior, integrated the Army, and the civil rights movement escalated its successes even as we escalated the Cold War and our presence in Vietnam. President Reagan built up the military even as he liberalized the economy.

Sure, Naomi Wolfe, Frank Rich and other leftists believe that the imperialistic war on terror has turned America into a police state. But if they were right, they wouldn't be allowed to say that.

Two compelling new books help explain why our "empire" is different from the Soviet or Roman varieties. Walter Russell Mead's encyclopedic "God and Gold" argues that Anglo-American culture is uniquely well suited toward globalism, military success, capitalism and liberty. Amy Chua's brilliant "Day of Empire" confirms why: Successful "hyperpowers" tend to be more tolerant and inclusive than their competitors. Despite its flaws, Britain was the first truly liberal empire.

America has picked up where the British left off. Whatever sway the U.S. holds over far-flung reaches of the globe is derived from the fact that we have been, and hopefully shall continue to be, the leader of the free world, offering help and guidance, peace and prosperity, where and when we can, as best we can, and asking little in return. If that makes us an empire, so be it. But I think "leader of the free world" is the only label we'll ever need or - one hopes - ever want.