"The war we fight today is more than a military conflict," Bush told thousands of veterans at the American Legion convention. "It is the decisive ideological struggle of the 21st century."
Bush described the current violence in the Middle East and the recently thwarted attack to blow up planes over the Atlantic Ocean as part of the same movement that resulted in the Sept. 11 attacks .
"As veterans you have seen this kind of enemy before," Bush said. "They are successors to fascists, to Nazis, to communists and other totalitarians of the 20th century. And history shows what the outcome will be.
"This war will be difficult. This war will be long. And this war will end in the defeat of the terrorists," Bush said.
Bush acknowledged the unsettling times _ marked by sectarian violence in Iraq, war along the Israel-Lebanon border and terrorists allegedly plotting to blow up planes between Britain and the United States.
"The images that come back from the front lines are striking and sometimes unsettling," he conceded. "When you see innocent civilians ripped apart by suicide bombs or families buried inside their homes, the world can seem engulfed in purposeless violence."
Bush said those who were responsible for bringing down the World Trade Center are united with car bombers in Baghdad, Hezbollah militants who shoot rockets into Israel and terrorists who wanted to bring down the flights between Britain and the United States.
"Despite their differences, these groups form the outline of a single movement, a worldwide network of radicals that use terror to kill those who stand in the way of their totalitarian ideology," he said. "And the unifying feature of this movement, the link that spans sectarian divisions and local grievances, is the rigid conviction that free societies are a threat to their twisted view of Islam."
"The world now faces a grave threat from the radical regime in Iran," the president said. "We know the depth of suffering that Iran's sponsorship of terrorists has brought. And we can imagine how much worse it would be if Iran were allowed to acquire nuclear weapons."
Bush delivered his starkest threat yet to Tehran.
"There must be consequences for Iran's defiance," he said, "and we must not allow Iran to develop a nuclear weapons."