She was the catalyst who set in motion a series of interconnected events that gave a revolutionary twist to the century's last two decades and helped mankind end the millennium on a note of hope and confidence. The almost universal acceptance of the market as indispensable to prosperity, the collapse of Soviet Union, the downsizing of the state on nearly every continent and in almost every country in the world — Margaret Thatcher played a part in all those transformations, and it is not difficult to see how any would have occurred without her.

Born in 1925, Margaret Hilda Roberts was an enormously industrious girl. The daughter of a shopkeeper, she studied on scholarship, worked her way to Oxford and took two degrees, in chemistry and law. Her fascination with politics led her into Parliament at age 34, when she argued her way into one of the best Tory seats in the country, Finchley in north London. Her quick mind (and faster mouth) led her up through the Tory ranks, and by age 44 she got settled into the "statutory woman's" place in the Cabinet as Education Minister, and that looked like the summit of her career. But Thatcher was, and is, notoriously lucky. Her case is awesome testimony to the importance of sheer chance in history. In 1975 she challenged Edward Heath for the Tory leadership simply because the candidate of the party's right wing abandoned the contest at the last minute. Thatcher stepped into the breach. When she went into Heath's office to tell him her decision, he did not even bother to look up. "You'll lose," he said. "Good day to you."

But as Victor Hugo put it, nothing is so powerful as "an idea whose time has come." And by the mid-'70s enough Tories were fed up with Heath and "the Ratchet Effect" — the way in which each statist advance was accepted by the Conservatives and then became a platform for a further statist advance.

She chose her issues carefully — and, it emerged, luckily. The legal duels she took on early in her tenure as Prime Minister sounded the themes that made her an enduring leader: open markets, vigorous debate and loyal alliances. Among her first fights: a struggle against Britain's out-of-control trade unions, which had destroyed three governments in succession. Thatcher turned the nation's anti-union feeling into a handsome parliamentary majority and a mandate to restrict union privileges by a series of laws that effectively ended Britain's trade union problem once and for all. "Who governs Britain?" she famously asked as unions struggled for power. By 1980, everyone knew the answer: Thatcher governs.

Once the union citadel had been stormed, Thatcher quickly discovered that every area of the economy was open to judicious reform. Even as the rest of Europe toyed with socialism and state ownership, she set about privatizing the nationalized industries, which had been hitherto sacrosanct, no matter how inefficient. It worked. British Airways, an embarrassingly inefficient national carrier that very seldom showed a profit, was privatized and transformed into one of the world's best and most profitable airlines. British Steel, which lost more than a billion pounds in its final years as a state company, became the largest steel company in Europe.

By the mid-1980s, privatization was a new term in world government, and by the end of the decade more than 50 countries, on almost every continent, had set in motion privatization programs, floating loss-making public companies on the stock markets and in most cases transforming them into successful private-enterprise firms. Even left-oriented countries, which scorned the notion of privatization, began to reduce their public sector on the sly. Governments sent administrative and legal teams to Britain to study how it was done. It was perhaps Britain's biggest contribution to practical economics in the world since J.M. Keynes invented "Keynesianism," or even Adam Smith published The Wealth of Nations.

But Thatcher became a world figure for more than just her politics. She combined a flamboyant willpower with evident femininity. It attracted universal attention, especially after she led Britain to a great military victory over Argentina in 1982. She understood that politicians had to give military people clear orders about ends, then leave them to get on with the means. Still, she could not bear to lose men, ships or planes. "That's why we have extra ships and planes," the admirals had to tell her, "to make good the losses." Fidelity, like courage, loyalty and perseverance, were cardinal virtues to her, which she possessed in the highest degree. People from all over the world began to look at her methods and achievements closely, and to seek to imitate them.

One of her earliest admirers was Ronald Reagan, who achieved power 18 months after she did. He too began to reverse the Ratchet Effect in the U.S. by effective deregulation, tax cutting and opening up wider market opportunities for free enterprise. Reagan liked to listen to Thatcher's various lectures on the virtues of the market or the minimal state. "I'll remember that, Margaret," he said. She listened carefully to his jokes, tried to get the point and laughed in the right places.

It was the beginning of a new historical age. All the forces that had made the 20th century such a violent disappointment to idealists — totalitarianism, the crushing of individual choice and initiative — were defeated. But the values that Thatcher had supported stayed: free markets and free minds. The world enters the 21st century and the 3rd millennium a wiser place, owing in no small part to the daughter of a small shopkeeper, who proved that nothing is more effective than willpower with a few clear, simple and workable ideas.