BERLIN — Niall Ferguson was here last week, promoting his latest book, Colossus: The Price of America’s Empire.

For those who don’t know him, Ferguson (whose first name is pronounced Neal) published three very well-regarded books in his first ten years out of Oxford: Paper and Iron: Hamburg Business and German Politics in the Era of Inflation 1897-1927, The World’s Banker: The History of the House of Rothschild, and The Pity of War: Explaining World War I, an intriguing argument that the English would have done better to let the Germans have their way with France in 1914.

The dilution began with The Cash Nexus: Money and Power in the Modern World 1700-2000. It continued with a six- part history of the British Empire for BBC television, and increased dramatically with the next two books, Empire: the Rise and Demise of the British World Order and the Lessons for Global Power (2002) and, now, Colossus. These last two are, in fact, pretty thin soup.

Nevertheless, the 40-year-old Scot has been hired by Harvard University’s history department, presumably in the hope that his best work is still ahead.

But when Ferguson visited the American Academy in Berlin last week, his arguments did not go over well. His proposal that the United States should more forthrightly accept a global burden, train a new corps of colonial administrators and settle down to govern in Iraq — and, by extension, Afghanistan, Haiti, Kosovo, Rwanda, wherever a stabilizing hand is needed — was met with skepticism on all sides.

And when his interlocutor read a passage from Colossus in which the author suggested that, in order to enforce this new world order, the US should vastly increase the size its army by drafting prisoners, illegal aliens and the unemployed, Ferguson’s response drew derisive laughter from the audience. He had managed to displease his German and American listeners alike.

This is, in truth, a remarkably difficult moment for the United States, in its embarrassment over the widespread prisoner abuse in Iraq. If American military police had not been prepared to act severely toward their more defiant captives, they would have been derided as innocents who didn’t know how to conduct a war against an army whose leadership had been hardened by a long bitter war with Iran. Since they acted brutally, they have been derided for having been inhumane (as indeed they were.)

Perhaps the single most telling fact about America was the existence of photographs themselves. It was reckless in the extreme to send those kids into battle, innocents and sadists alike, bristling with weapons and global positioning devices and digital cameras with which to record the boredom and the horror — but otherwise almost completely lacking in dependable Iraqi counterparts and unequipped with a working vision of the end they were fighting to achieve.

Yes, it may even now work out, at least better than is commonly expected. The stain on America’s reputation, however, will be permanent.

Thus the best summary of the war so far was offered by an anonymous soldier. When it was pointed out by an Iraqi that the man over whose head he was slipping a sandbag wasn’t anti-American, he answered, “Well, I guess he is now.”

The question is, Is it helpful to understanding all this to call America an empire?

The Bush administration is adamant that it is not (“America has never been an empire,” George W. Bush asserted as a candidate. “We may be the only great power in history that had the chance and refused.”)

Ferguson is completely unconvincing that it is.

So, for the most part, is the rest of the ever-lengthening shelf of books at one end of which sit The Rise and Fall of the Great Powers by Paul Kennedy and The End of History by Francis Fukuyama.

Indeed, in a review of Colossus in the current New York Review of Books, historian Kennedy notes that Ferguson relies on the appearance in recent years of “the many writings that define empire in more nuanced terms than the classical Roman juridicial definition (i.e. empire is now seen more as the exertion of undisputed influence than as the formal annexation of another land.)”

It depends, then, on the meaning of “undisputed.” Surely the new nuanced definition more nearly describes the former Soviet Empire than the United States.

But if the US is not an empire, what is it?

It’s worth recalling how the concept of “empire” entered the political lexicon in its present form. It was in 1902 that a veteran correspondent for the Manchester Guardian, J.A. Hobson, wrote a book, “Imperialism,” to describe its pursuit, and the word and its analytic framework entered the language.

“Nationalism, internationalism, colonialism, its three closest congeners, are equally elusive, equally shifty,” wrote Hobson, “and the changeful overlapping of all four demands the closest vigilance of students of modern politics.”

In 1902, three powerful nations of northern Europe — Great Britain, Germany and France — were arrayed against each other on terms of rough equality, engaged (with other European states) in a gigantic global land grab. From their internecine struggles emerged a pair of new great powers, the United States and the Soviet Union. They contended for half a century, before the Russia-dominated confederation collapsed.

The United States today is immensely powerful. But it is not an empire — not even when you’ve got a sandbag over your head. Instead it is a dominant player in a relatively open global system in which there are many other active participants. In its periodic attempts to intervene in distant places — Lebanon, Panama, Kuwait, Mogadishu, Haiti, Kosovo, Afghanistan, Iraq — it is sometimes reluctant and inept. American influence in other dimensions — cultural, financial, economic, political — though extensive, is no more unbounded than its military might.

It may be that there is no better word for this than “superpower” — a term defined mostly in opposition to the will of other superpowers. Nor is it likely that the US will remain the only superpower for very long. China at last is in the wings.

Modern technology and global growth have greatly changed the rules. The boyish game of empire that Hobson analyzed a hundred years ago and that Niall Ferguson recommends today is no longer played. Something much more complicated is has taken its place.