The United States is a "danger to the world" because of its denial that
it is a military and economic empire, according to Niall Ferguson,
historian and new-found darling of the American right.

Prof Ferguson is author of Empire: How Britain Made the Modern World,
the book whose tie-in TV series controversially concentrated on the
liberalising latter days of the British empire. He said that America's
refusal to admit to "what it was" meant it risked never learning the
lessons of British expansionism.

"The United States is the empire that dare not speak its name. It is an
empire in denial, and US denial of this poses a real danger to the
world. An empire that doesn't recognise its own power is a dangerous one."

Prof Ferguson passed up a dinner invitation from the US secretary of
state, Colin Powell, to address the Guardian Hay Festival.

He told his audience that, with military bases in three-quarters of the
countries of the world, and 31% of all wealth, America made the British
empire at its zenith in 1920, when a quarter of the globe was pink,
look "like a half-baked thing".

But he warned that America was too much of a military empire to last,
too fond of short-term interventions in Haiti, Lebanon and now Iraq that
lacked "sustained commitment to the dirty work of rebuilding".

"As Iraq is showing, military commands cannot create law and order.
Their job is to kill people. The British empire learned that the military
must be subservient to civilian power if you are to build civil
administrations."

America's critical weakness, however, was its fatal lack of
self-knowledge, he said. "When you talk to Americans about empire they say, 'but
we came into existence to fight imperialism.'

"US defence secretary Donald Rumsfeld famously told al-Jazeera 'we
don't do empire'. But how can you not be an empire and maintain 750
military bases in three-quarters of the countries on earth?" He argued that
"Britain had an amazing capacity for self-criticism, even when the empire
was at its height.

"The Americans simply don't believe they are there. But since they
annexed the Philippines in 1898, they have acted as an imperial power."

Furthermore, he insisted, the people who were "now in charge of the
defence department have grabbed September 11 as a chance to push through
the imperial agenda". But only a few, on the neo-conservative right,
were prepared to use the e-word publicly.

Prof Ferguson, professor of economics at New York University after
leaving Oxford, said he did not see the concept of empire as necessarily a
bad thing. "In all kinds of ways the British empire from the 1850s
onwards was an incredibly liberal one. For all the warts on its face it
created a free enterprise global economy, protected women and stopped
infanticide in India, and ultimately brought representative democracy. I
believe a liberal empire can do good."

The plight of most of Africa's states which were former colonies was
dramatically worse than at independence. But he doubted the US could be a
"better liberal empire that learns from Britain's mistakes, even though
the US is vastly more prosperous and militarily strong than Britain
ever was."

He compared the "unique situation" the US felt it was in now in Iraq
with a proclamation the British made on entering Baghdad in 1917: "Our
armies do not come into your lands and your cities as conquerors, but as
liberators..."

Prof Ferguson said the concept of "conquest as a form of liberation, of
building an empire of democracy, is not new. Britain did it too in its
liberal heyday. What we are looking at is a second Anglophonic empire
similar in many ways to the first, and that has to be recognised."

Security men removed a self-styled "shamanistic poet", Niall McDevitt,
from the lecture, when he accused Prof Ferguson of trying to "alleviate
guilt" [about the empire], while reciting a poem in pidgin on the
imperial legacy in the New Hebrides islands in the Pacific.

"I know you are Irish," Prof Ferguson told him, "but what is your
question?"