The opening moves of a US-led assault on the rebel-held town of Falluja end a seven-month stand-off that both US and Iraqi interim government officials found intolerable.
Since Washington called off an earlier offensive in April, US and Iraqi officials say, the rebel stronghold has been both an unacceptable challenge to the government's authority and a refuge for radical Islamists bent on destabilising the country.
But the attack carries the risk of a political and military backlash that could make swathes of central Iraq virtually ungovernable.
Before launching the assault, Iyad Allawi's interim government considered two other options - negotiating with representatives of Falluja to persuade them to turn over the more radical insurgents and accept government authority, or isolating the town.
Peace talks failed, according to the government, because local negotiators could not force an agreement against the will of the hardliners in their midst.
Leaving the town in rebel hands, meanwhile, would undermine the legitimacy of parliamentary elections scheduled for January. Militants would be able to use the city as a base from which to launch attacks aimed at scaring off voters.
However, to many Iraqis, the risks of an assault far outweigh the benefits. During last April's offensive, Sunni Arabs with tribal and religious ties to the city launched a wave of solidarity attacks on US supply columns and on other targets across central Iraq.
That wave of violence never really subsided, particularly in the Euphrates valley towns north and west of Falluja.
The attack also led to a radicalisation of the rebel movement, with the Tawhid wa al-Jihad organisation of Abu Musab al-Zarqawi, a hardline Jordanian militant, turning itself from a marginal underground movement to a network operating in the open in several cities.
There are already signs of a similar upsurge in violence, with a string of car bombs, raids on police stations, and other insurgent attacks leaving more than 60 dead at the weekend in what has been seen as an attempt to take pressure off Falluja.
The April assault also had a political fall-out, as reports of massive civilian casualties in Falluja united Sunnis and Shias against the US military occupation. A threat by members of the Iraqi Governing Council - appointed by the coalition to assist their administration of the country - to resign was reportedly a big factor behind Washington's decision to call off the attacks.
Although no resignation threats have been issued this time, many of Mr Allawi's allies have come out strongly against a Falluja offensive - including President Ghazi al-Yawer, a Sunni Arab tribal leader.
Public outcry over the Falluja attack may make it difficult for Sunni Arab groups to make alliances with Mr Allawi in the run-up to the January elections, or to participate in a government over which he presides.
Mr Allawi may believe he can avoid mistakes made by the coalition in April. US forces have prepared carefully for the assault, while at the same time leaving the insurgents off-balance with a series of air strikes.
A second conflict with followers of the radical Shia leader Moqtada al-Sadr that stretched US resources in April was resolved politically, with Sadr loyalists vowing to turn themselves into a peaceful opposition.
Whereas in April Iraqi forces mutinied after being thrown into battle, this time they have been carefully integrated with US troops.
Mr Allawi's government is also apparently managing the media's portrayal of the fighting. His government's forces aim to dilute public perceptions of a foreign assault on an Iraqi town.
Among their first objectives has been the town's hospital, the source of reports of massive civilian casualties during the first attack, which US officials have claimed were rebel propaganda.
However, even a model offensive may not bring stability. In what was widely seen as a rehearsal for Falluja, US and Iraqi forces recaptured the rebel-held town of Samarra in a lightning offensive in October.
The US military claims it killed more than 100 insurgents and captured dozens more at the cost of only one fatality and the fighting was over before TV stations could show damaged homes and civilian dead.
Samarra, however, remains far from pacified. Locals say an Iraqi National Guard garrison brought in from the outside is feuding with a corrupt police force. In the meantime, they say, the most prominent insurgent leaders simply went to ground or fled.
