In the latest stage of an American troop pullout by the end of 2011, U.S. forces withdrew from Iraqi cities and towns last week.

As U.S. soldiers redeployed to bases outside urban areas, Iraqis expressed their pleasure at this increase in their sovereignty with parades. Many prayed that their own military can keep Iraq safe.

We hope so, too, and that the Iraqi army and national police, 600,000 strong, will do its job. Once chided for quitting battle, Iraqi soldiers have displayed considerable ability and poise in the military campaigns ordered by President Nouri al-Maliki in the last couple of years. Their training by U.S. troops appears to have been largely effective.

Notwithstanding that, the insurgency has not disappeared. It remains unclear whether it can turn occasional suicide attacks and car bombs into the sectarian strife that led to the brink of civil war three years ago. In 2006-07, before the U.S. surge turned it back, al-Qaida unleashed a spiral of revenge attacks between Sunnis and Shi’ites that ripped apart a fragile, post-Saddam society.

The recollection of that horrible year or so of neighborhood-by-neighborhood terror should persuade Iraqis of all stripes to abhor the idea of a repetition.

The status-of-forces pact negotiated by the Bush administration and wisely embraced by the Obama administration permits U.S. troops to return if needed to assure that America’s sacrifice on Iraq’s behalf was not in vain.

This nuanced redeployment of the American safety net poses a challenge and an opportunity to Iraq’s democracy. The U.S. troop pullout does create an opening for the insurgency. If the danger increases, so will the duty of the Iraqi government and people to respond to provocation with cool heads. Major political issues and sectarian mistrust remain to be fought over — not just at the ballot box but through peaceful competition and compromise that are also taking hold in Iraq. Their continuation is the best strategy to secure the insurgency’s eventual evaporation.

Yes, U.S. troops can return if needed, but the heavy lifting must now be done by Iraq.