President Bush has told the UN General Assembly civilisation itself is threatened by international terrorism.
He warned terrorists would use chemical, biological and nuclear weapons as soon as they acquired them.
And he said all nations must now unite to defeat the "evil" of terrorism because it threatened all of civilisation.
"Civilisation itself, the civilisation we share is threatened," President Bush told the assembly of 48 government leaders and over 100 foreign ministers.
"History will record our response and judge or justify every nation in this hall.
"They can be expected to use chemical, biological and nuclear weapons the moment they are capable of doing so."
He said the attacks of September 11 were so terrible they "offended humanity itself."
He told the meeting at the UN headquarters in New York, "A few miles from here many victims are still lying in a tomb of rubble."
And he warned the terrorists were now planning further strikes, "Perhaps in my country, perhaps in yours."
"However long it takes, the hour of justice will come," he added. "We must unite in opposing all terrorists not just some of them. The only alternative is a nightmare world where every city is a potential killing field.
"They hate not policies but our very existence."