Japanese voters went to the polls Sunday with one overriding aim — to bring an end to more than a half-century of nearly uninterrupted one-party conservative rule. The monumental victory handed to the opposition Democratic Party of Japan (DPJ) marks a quiet revolution in the politics of America's most important Asian ally.

This is more than a simple power shift. It ushers in a competitive, two-party democracy in which politicians and their constituents may finally have more say in shaping Japanese policy than bureaucrats and businessmen. Neither Japanese voters nor the DPJ seek radical change. They want to invigorate a sclerotic system that has been unable to respond to the challenges of a global economic slowdown, an aging society and the rise of Japan's long-time rival, China.

The architect of this election triumph is an unlikely, and widely misunderstood, revolutionary leader: Ichiro Ozawa. The victory fulfills a strategy that Ozawa presented in remarkable clarity in his 1993 manifesto, "Blueprint for a New Japan," which he wrote while he was a senior leader of the long-ruling Liberal Democratic Party .

"Postwar Japanese politics has been, fundamentally, quite cozy and undemanding," Ozawa wrote. "While Japan concentrated on its own economic development and the distribution of its newly generated wealth, it left the maintenance of international order to the United States. "

The end of the Cold War meant Japan should share responsibility for global security, Ozawa argued, a conviction hardened by his failure to get Japan to send forces as part of the international coalition in the Persian Gulf War. He called for Japan to become a "normal nation," finally freed from its postwar dependency on the United States. This required "the end of Japan's consensual, deal-making politics."

Ozawa spearheaded two key reforms. While he was still in the LDP, he pushed through a law that allowed Japan to dispatch troops overseas for the first time since World War II, in U.N. peacekeeping missions. After leaving the party in 1993, triggering the formation of a short-lived opposition government, Ozawa helped create a new system of single-member electoral districts to foster real competition and majority rule.

Ozawa, whom I have known for more than 20 years, is a controversial and contradictory figure. In many ways, he embodies the system he has sought to destroy. He is the master of the backroom deal, uncomfortable with the media and almost anti-charismatic. Ozawa inherited the parliament seat of his father in rural Iwate prefecture; he learned how to build local political machines as the protege of Japan's most notorious political boss, Kakuei Tanaka.

Ozawa's first attempt to break the LDP's monopoly foundered in part because of his own arrogance. He wandered in the political wilderness until he joined the DPJ in 2003, leading it to a succession of election victories, made possible by the electoral-district reform. He built an electoral machine using old alliance-building techniques while recruiting a new generation of politicians ready to run policy-based campaigns.

Ozawa reluctantly stepped aside as party leader in the spring, under the cloud of charges of illegal political fundraising. Nonetheless, he will wield more influence than any other single person, including the prime minister, over Japan's future direction.

Some worry that a DPJ government may undermine the U.S.-Japanese security alliance. But Ozawa and the DPJ are deeply committed to a strong relationship, even if they take a different path now and then. For the United States, there is a greater value in a government that can stimulate policy-making in Japan.

This revolution, like any, carries risks. The predictability of the past may be lost, and the DPJ may not be up to the task of governing. But, after a long road, an opportunity for real change in Japan has arrived.

Dan Sneider, a former foreign correspondent for the Christian Science Monitor, is associate director for research at Stanford University's Shorenstein Asia-Pacific Research Center. He wrote this commentary for The Washington Post.