More than six years after invading Iraq and deposing its leader, Saddam Hussein, U.S. combat forces have withdrawn from Iraq's cities. The redeployment is an important step forward in the reclamation of Iraqi sovereignty, and a political victory for Iraqi Prime Minister Nouri al-Maliki.

The move is not a complete withdrawal, however. U.S. forces have been moved outside the cities and can return if requested. Trainers and advisers also remain in the urban areas. The question now is whether Iraq's security forces can keep the peace — not only against insurgents who oppose Mr. al-Maliki but also by preventing sectarian violence against the Sunni minority.

The clock has been ticking toward a U.S. withdrawal since then U.S. President George W. Bush launched the "surge" — a massive influx of American combat forces to stabilize Iraq — in May 2007. After an initial and expected spike, violence in Iraq has diminished, allowing the Baghdad government to consolidate its own power and authority. The election of Mr. Barack Obama, who had campaigned on a pledge to withdraw U.S. forces, provided a new urgency to the Iraqi task of taking responsibility for the country's security.