By the time the Vietnam war ended in 1975, it had become America's longest war, shadowed the legacies of four presidents, killed 58,000 Americans along with many thousands more Vietnamese, and cost the U.S. more than $660 billion in today's dollars.

By the time the bill for World War II passed the $600-billion mark, in mid-1943, the United States had driven German forces out of North Africa, devastated the Japanese fleet in the Battle of Midway, and launched the vast offensives that would liberate Europe and the South Pacific.

Difficult times: Abas Mahmoud prepares tea on an open fire inside his home in Baghdad. Iraqis have been plagued by electricity cuts, shortages of petrol and cooking oil as the Americans and the Iraqi government have been unable to restore basic services to pre-war levels due to sabotage and insurgent attacks. (AP)

The Iraq war is far smaller and narrower than those conflicts, and it has not extended beyond the tenure of a single president. But its price tag is beginning to reach historic proportions, and the budgetary "burn rate" for Iraq may be greater than in some periods in past wars.

If U.S. involvement continues on the current scale, the funding for the Iraq war — combined with the conflict in Afghanistan and other foreign fronts in the war on terrorism — is projected to surpass this country's Vietnam spending next year.