US Defence Secretary Donald Rumsfeld has said that his country has entered a new era in which it must pre-emptively seek out and prevent attacks by terrorists and terrorist states.
Rumsfeld: 'We are not going to climb into holes and hide'
He told coalition troops at US Central Command in the Gulf state of Qatar that the wars in Afghanistan and Iraq showed that America had made a good start.
He said the US-led invasion of Iraq would go down in military history because of its unprecedented combination of power, precision, speed and flexibility.
It was also notable for its compassion towards innocent civilians, he said.
His comments came after US military officials were reported as saying that American air operations in the region would be run from Qatar rather than Saudi Arabia for the foreseeable future.
BBC Middle East analyst Roger Hardy says the war in Iraq showed that Saudi Arabia was unwilling to accept a high-profile American presence on its soil.
Baghdad was liberated in less than a month, possibly the fastest march on a capital in modern military history
He adds that the country's de facto ruler, Crown Prince Abdullah, is thought to have wanted to reduce the US military presence in Saudi Arabia for some time.
In his address to the troops, Mr Rumsfeld said: "The task we have is a different one in the 21st century - it is not
conventional, it is unconventional.
"It requires us to seek out and defend and prevent the attacks by
"It may be an untidy world, but our country and our friends and allies are going to be able to preserve our way of life, continue our way of life, not climb into holes and hide."
To cheers, Mr Rumsfeld told the troops that what they had done would go down in
"Those scenes we have all witnessed of free Iraqis pulling down statues of Saddam Hussein, greeting coalition forces and celebrating their new-found freedom - they will certainly take their place alongside the fall of the Berlin Wall and the liberation of Paris and each of you helped make that happen.
"You can be very proud of it.
General Tommy Franks won plaudits from his civilian boss
"You have helped rescue a nation and liberate a people.
"You have driven a repressive regime from power, ending a threat to free
people everywhere, protecting our country from a growing danger and giving the Iraqi people a chance to build a free nation."
Mr Rumsfeld hit back at critics of the war in Iraq by paraphrasing Winston Churchill's comments about the Battle of Britain, saying: "Never have so many been so wrong about so much".
He praised General Tommy Franks, the commander of the coalition forces in Iraq, and all of the men and women who served under him.
"Baghdad was liberated in less than a month, possibly the
fastest march on a capital in modern military history," he said.
Mr Rumsfeld is on a tour to thank Gulf leaders for their support during the war.
He is expected to visit Afghanistan later this week. A trip to Iraq could also be included in his schedule.