President George W. Bush likened the U.S.-led wars on terror and in Iraq to the Second World War and the Cold War.

"The war on terror is civilization's fight. And, as in the struggles of the last century, civilized nations are waging this fight together," Bush told U.S. Air Force graduates on Wednesday.

"This is the great challenge of our time, the storm in which we fly," he said.

Bush was giving the commencement speech at the graduation ceremony of an Air Force Academy in Colorado Springs, Colo.

But while he was addressing U.S. cadets, Bush's speech was also aimed at an international audience increasingly skeptical about the U.S.-led war on terror and its avowed goal to bring democracy to the Middle East.

"The enemies of freedom are opposed by a great and growing alliance," Bush claimed, invoking the Allied struggle against Nazism and Communism in the last century.

"Nations that won the Cold War, nations once behind an Iron Curtain, and nations on every continent see this threat clearly," he said.

His remarks came on the eve of the president's European trip to gather support for U.S. plans in Iraq.

Bush's trip includes visits to Italy on Thursday and later France. There he will attend on the weekend the 60th anniversary commemoration of the Allied Forces' D-Day landing in Normandy, which led to Nazi Germany's defeat.

Italy is a key ally with troops in Iraq, while France was among the staunchest opponents to the war.

Security council member France is demanding changes to the U.S.-British draft United Nations resolution laying out the terms of Iraqi sovereignty and UN involvement after the handover of power on June 30 to an Iraqi government.

President Vladimir Putin of Russia, another UN security council member, with doubts about U.S. Iraq plans, will also attend the D-Day ceremonies, as will German chancellor Gerhard Schroeder, another original opponent of the Iraq war.

The U.S. is seeking to share its financial and human burden – it's struggling to maintain about 140,000 troops in Iraq – by winning major troop commitments for an international military stabilization force for Iraq.

"It is essential that he get troop and resource commitments for our mission in Iraq to relieve the burden on our troops, to help achieve the stability ... and internationalize the presence on the ground," the Democrats' presidential contender John Kerry said in response to the speech.

Bush's speech was one in a series he's delivering about the war on terrorism and Iraq ahead of the transfer of political power in Baghdad.