The State Department has issued yet another warning to Americans traveling abroad. Rumors of suspected terrorist attacks are circulating within the United States. A mild panic, sure to affect New Year's Eve events, is underway despite the White House saying it has "no specific information about targets." A chilling symmetry announces itself: The century that began in terrorism is threatening to end the same way.

To my mind, the 20th century really began with Gavrilo Princip, a Bosnian Serb and a member of a secret society, the Black Hand. On June 28, 1914, he assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian empire, and his wife, Sophie. "Es ist nichts" (It is nothing), the archduke kept saying as he died. But he could not have been more wrong. His murder precipitated World War I.

It's conceivable Europe would have had its great war in any case. But it is also conceivable that, absent what German Chancellor Otto von Bismarck had presciently called "some damned foolish thing in the Balkans," the war might well have been avoided. To this day, historians puzzle over the war and how it started. It made little sense.

But the plunge into chaos and carnage was swift and the consequences both catastrophic and enduring. The Russian, German, Ottoman and Austro-Hungarian empires collapsed. Communism rose in Russia and, eventually, controlled all of Eastern Europe, threatening Western Europe for a time as well.

Adolf Hitler, a veteran of the Eastern front, seized power in a weakened and dazed Germany. World War II and the Holocaust followed.

Even the winners lost. Britain and France were never again the great powers they had been. France, in particular, had been bled white, a nation of war-wounded that was supine later in the face of the looming Nazi threat. The financial markets moved west to the stability and wealth of New York and remained there even after the stock market collapsed in 1929.

It is both good and instructive to end this century by honoring its great men--the leaders, the inventors, the scientists, the artists. It has been a remarkable century in that regard--Roosevelt, Mandela and Einstein just for starters. These are people who enrich our lives, show us how to live--what is possible. We need heroes. Even atheists need gods.

But more and more we are beginning to recognize that this is preeminently the century of the common man. Often he is good and worthy--the heroic nobody of Aaron Copland's stirring fanfare, the GI of World War II, the indomitable farmer of the dust belt, the immigrants who keep coming here, the unknown "tank man" of Tiananmen Square, and the geeks who took an insight and some garage space and created an industry. But Princip would smirk at that list. It is his century, too.

It was also "ordinary men," the very title of Christopher Browning's great Holocaust book, who murdered the Jews of Europe. It was ordinary men who killed John F. Kennedy, Robert F. Kennedy, Martin Luther King Jr., John Lennon. The ordinary struck down the Gandhis in India and Yitzhak Rabin in Israel. Each and every act changed history--and the terrorist knew it. Each could, with a single act, nullify an election, rebuke an entire movement--turn back history itself. With our neat weapons, we have empowered the powerless and turned losers into instant winners.

Caesar was assassinated, I know, and Lincoln, too. Terror is not unique to this century. But it is, I think, more common, more pervasive. Partly this is because governments can be held hostage to the consequences of their actions. The United States and the Soviet Union did not fight, because war was, simply, inconceivable. Terrorists, however, have no constraints. The worse the consequences, the better the outcome for them.

We feel less and less secure in our own country. Who is this Ahmed Ressam, arrested in Washington state last week with bomb-making materials? What was he up to? Have others like him already gotten into the country? Down deep, we know the government can only do so much. We can't even stop kids from coming into schools with guns and bombs. How could we possibly seal the border? We are a trading nation. Goods come in, goods go out. So do other things.

So the century ends with a furrowed brow. We are concerned, we are worried. We are learning the difference between terrified and terrorized--between a passing fright and one that lingers. New Year's plans are being changed, a concession to terrorism right there. The common person, hero of the century and parents to us all, recognizes his enemy. It is the common person.