The unique quality of America's fifth major war of this century was established instantly: The government still had the power to unleash war but no longer the ability to control how or when its citizens would learn about it. This time, Americans learned they were at war from the point of view of the country its forces were attacking.

It was the first major war since the Mexican War in 1846 in which America clearly initiated the hostilities, although President Bush could claim it was Iraqi President Saddam Hussein's aggression that caused the conflict. It was also the first war that America began under a deadline -- one of its own making designed to pressure the adversary, but which in the end forced America's own hand.

Therefore, there were no surprises about the beginnings of this war. The nation had been debating it, preparing for it, and anxiously awaiting it for more than five months.

By contrast, many of America's earlier wars took the country by surprise. In 1898, the sinking of the battleship Maine became the trigger -- or as many scholars now argue, the pretext -- that initiated what Secretary of State John Hay called America's "splendid little war" with Spain. On Dec. 7, 1941, the date President Franklin Delano Roosevelt proclaimed would "live in infamy," Americans got the news of Japan's sneak attack on Pearl Harbor on a sleepy Sunday and then followed bulletins while huddled around their radios.

In 1950, the Korean War began when North Korean troops flooded across the 38th parallel in a sudden invasion that became the first test of America's willingness to go to war to check communism. That war was the first since the War of 1812 that ended not in glorious American victory but in frustrating stalemate.

It was followed by the even more embittering, and disillusioning, Vietnam experience.

Throughout their history, Americans had become conditioned to think of themselves as winners. Vietnam changed that. Its 11 years of escalating violence divided the nation as had no conflict since the Civil War. It ended in defeat and left a legacy in which Americans and their leaders vowed never again to wage war without clear objectives, a united country, and a determination to win.

Bush cited that experience in his address to the nation last night and repeated his promise that "this will not be another Vietnam."

The war against Iraq already differs vastly from that waged in Southeast Asia. Since Aug. 2, when Iraq invaded Kuwait, Bush built the largest military force since Vietnam, this time before the war started. There was no gradual Vietnam-style escalation. The objective, too, was clear and narrow: to drive Iraqi forces from Kuwait.

This time, in short, there would be no "strategic hamlets," no "pacification," no "search and destroy" missions, no Ho Chi Minh trail offering jungle sanctuary for enemy supply lines.

This time, moreover, the United States went to war with support from the United Nations -- and not in the face of scorn from much of the world. And this time, the president had won the backing, narrowly but unequivocally, for war from Congress.

Other differences from Vietnam were less heartening for Bush. Vietnam began with an American economy that was robust and with most Americans sharing President Lyndon B. Johnson's belief that the United States could not only create a Great Society at home but also export it, even to Vietnam.

This time, it is an inward-looking United States that goes to war. The nation is gloomy about its economic prospects. And it begins war just 14 months after the collapse of the Berlin Wall heralded the country's triumph over communism, which most Americans hoped would end the era in which U.S. troops would be asked to fight at distant points on the globe. The end of the Cold War instead has seemingly cleared the way for a new and less predictable form of conflict.

There was also a parallel between Bush's declaration that this war would pave the way to "a new world order" and President Woodrow Wilson's promise that World War I would "make the world safe for democracy." The idealism implicit in both pledges is deeply rooted in U.S. history. But so is the disappointment that met Wilson's illusory hopes.

On the first night of war, the news from the front was positive. The great war machine that had been built during the 1980s seemed to be working.

But in the end it was still war. If there's one lesson from American history that applies now, it is

that Americans quickly grow weary of war. With television bring- ing its horrors home so intimate- ly, that weariness, not Iraqi

forces, could be Saddam's greatest asset.