By James Westhead
BBC News, Washington
On the fifth anniversary of the 11 September attacks, President George W Bush warned Americans they were in "a struggle for civilisation" that would be determined in part by the war in Iraq.
The primetime address was the fifth of Mr Bush's presidency
"The safety of America depends on the outcome of the battle in the streets of Baghdad," said Mr Bush.
In a nationwide broadcast from the Oval Office, he said the global war on terrorism would determine the course of the 21st Century and affect the lives of millions of people.
"If we do not defeat these enemies now, we will leave our children to face a Middle East overrun by terrorist states and radical dictators armed with nuclear weapons," Mr Bush said.
The primetime television address was only the fifth Mr Bush has made during his presidency.
Tyranny and freedom
In solemn tones, he evoked the suffering and praised the courage of Americans on that day five years ago, but devoted most of his speech to a defence of his actions since then, from the war in Iraq to domestic surveillance programmes, to his freedom agenda in the Middle East.
Mr Bush's main aim appears to be to frame the unpopular war in Iraq within a broader context of his war on global terror and even more than that - an epic battle between tyranny and freedom.
The president described the war on terror as the decisive ideological struggle of the 21st Century - comparing it to World War II and the Cold War against the Soviet Union.
His language was particularly forceful, even apocalyptic, with warnings of a radical Islamic network "determined to bring death and suffering to our homes".
The president had pledged that his speech would not be political. However, he implicitly challenged Democrats who have opposed his policies in Iraq by insisting the threat would require a unified country to achieve victory.
"We must put aside our differences, and work together to meet the test that history has given us," he said.
Nevertheless the address drew sharp criticism from political opponents.
Senator Edward Kennedy - a leading Democrat - said the president "should be ashamed of using a national day of mourning" to justify his Iraq policy.
Another top Democrat, Senator Charles Schumer of New York, called the address disappointing, saying: "You do not commemorate the tragedy of 9/11 by politicising it."
The country is less than eight weeks away from a crucial mid-term election that could strip control of Congress from the Republicans for the first time in a decade.
Mr Bush's strategy appears to be to try and neutralise criticism of his invasion of Iraq by linking it in with the "war on terror".
It is politically risky as most Americans tell pollsters they believe Iraq was - in retrospect - a dangerous diversion. However, Mr Bush argues that stabilising Iraq and establishing democracy is now the most important element in protecting America.
It is unlikely he will convince many of his political opponents who believe his actions since 11 September 2001 - especially in Iraq - have harmed rather than enhanced national security.