Yet this long awaited collision has ignited the most sustained Iraqi revolt against the occupation since it began a year ago, raising the spectre of a future the US had been desperate to avoid: a Shia Muslim uprising joining forces with what till now had been a Sunni dominated resistance.
It is unclear who most wanted this fight - the Americans or Muqtada Sadr. It is clear who started it.
On 28 March 2004, American soldiers closed Sadr's al-Howza newspaper (circulation just 10,000) for "incitement to violence", specifically for an article that likened the US proconsul in Iraq, Paul Bremer, to Saddam Hussein. Five days later they arrested Sadr's main man in Najaf, Mustafa Yaqoubi, for the killing a year ago of Abdul Majid Khoei, a rival Shia cleric who had returned from exile after the war. They also laid siege to several of Sadr's offices.
Sadr viewed these actions -and their timing - as preludes to elimination. Bremer, who was bereft of any military plan, according to US military sources, assumed Sadr would meekly back down, as he did during a stand off last year. Instead, Sadr mobilized his black-suited Mahdi Army to march in martial but non-violent demonstrations.
On 4 April, defiance became urban warfare, after Sadr militiamen tried to storm a garrison of Spanish troops near Najaf. In the ensuing week, similar battles raged over the institutions and symbols of political power in the southern cities of Kufa, Amara, Kut, Nasariyah, Karbala, Basra and the Shia-dominated Baghdad districts of Sadr City, Kadamiya and al Shoala, leaving hundreds dead, the majority of them Iraqis.
Did Sadr light the fire? Once begun - and sensing the accumulated sense of frustration among his people -he did nothing to douse it. "There is no use for demonstrations, as your enemy loves to terrify and suppress opinions, and despises peoples," he said. "Intimidate your enemy, as we cannot remain silent over his violations."
"We have a group under Muqtada Sadr that has basically placed itself outside the legal authorities, the coalition and Iraqi officials," Bremer answered. "Effectively he is attempting to establish his authority in the place of the legitimate authority. We will not tolerate this".
Within hours, an Iraqi judge had issued an arrest warrant for Sadr for the murder of Khoei, though Iraq's current interim Justice Minister questioned its legality. Sadr shrugged off the attempt to criminalize him and his revolt. The uprising would continue, he vowed on 6 April, "until our cities are free of the occupiers and our prisoners are released".
Sadr then moved from his mosque in Kofa to his Najaf offices, while his militia drove out Ukrainian soldiers from Kut, negotiated an uneasy détente with the Italians in Nasariyah and skirmished with Poles in Karbala. US soldiers re-took some parts of Kut on 9 April after rocketing its abandoned police stations, the first shots of a "sustained campaign until Muqtada Sadr turns himself in or his militia is destroyed," promised General Ricardo Sanchez, the chief US military commander in Iraq. He also dispatched massive US troop reinforcements to the south.
He will need more than force in Najaf, Kufa and Karbala, which are home to the Shia's holiest shrines. These cities are also the heart of a Shia religious establishment whose authority Sadr disdains but whose protection he seeks and whose quiescent attitude to the occupation, he seeks to challenge. Sadr's militia now guard the Najaf offices of Grand Ayotallah Ali al Sistani (and just about every other religious and political institution in the city), vanquishing not only the Iraqi police and occupation soldiers but also the other Shia militias. Sistani has expressed sympathy with the Sadr revolt, though not always with its means.
"In one week," observed Iraqi political analyst Gailan Ramis, "the Americans have turned Muqtada Sadr from one Shia cleric among others into the most significant political force in the land".
Why did they do it? There is little doubt that Sadr and his supporters have engaged in a conscious, confrontational struggle for political power with American-appointed authorities in his urban strongholds in Baghdad and southern Iraq. He has swelled the Mahdi Army from a force mustering barely 500 last August to one now commanding 10,000 men, armed with rocket-propelled grenades, mortars and light weapons.
But he is hardly alone. Take a trip through any of the Shia dominated southern cities and you will find militias belonging to one or other of the main Shia clerics and religious political parties in an open power struggle between themselves and the Iraqi police and occupation soldiers. In the central regions of Falluja and Ramadi (as the resistance testifies) it is armed Sunni groups, nationalist, Islamist and tribal, which rule. Go to the north and it is the Kurdish parties and their peshmergar guerrillas that hold sway, though they sometimes wear Iraqi police uniforms.
The charge that Sadr is attempting to "establish his authority in place of the legitimate authority" cuts little slack with most Iraqis, if only because in larges swathes of Iraq there is no one legitimate national authority to replace. Rather the decision to crush Sadr seems driven less by the threat he poses to the new Iraqi order than by his opposition to American power.
It is a force already wounded in Iraq by its abject failure to curb the Sunni insurgency and outraged by a visceral anti-Americanism exhibited in the lynching of four private US security contractors on 31 March. Bremer apparently viewed Sadr as a soft target, a lesson that could be taught to all Iraqis. It was a "colossal blunder", says Iraqi political analyst Wamid al Nithmi.
"I think the Americans decided to act against Sadr as a kind of pre-emptive strike. It was done not only to ensure a smooth passage to Iraqi sovereignty but also - and far more importantly, as far as the Americans were concerned - to ensure quiet in Iraq ahead of the US presidential elections in November. What Mr Bremer clearly did not see was that the Shias were a dry wood waiting to ignite. The move against Sadr - combined with anger at the assault on Falluja - provided the spark for the first widespread Shia rejection of the occupation".
The cost of this political miscalculation has already been enormous - not least to the American plan for Iraq. Fundamentally it has undermined the implicit contract on which that whole project depended. Underwritten by Sistani and maintained by the Shia religious parties (including, in practice, Sadr's), this held that in return for democratic elections, protest among Iraq's Shia majority would be confined to what Hamid Bayati, spokesperson for the Supreme Council for the Islamic Revolution in Iraq, a Shia religious movement, called "negotiation and peaceful means."
That deal was already under strain after the March massacres in Karbala and Baghdad, when 170 Iraqi Shias lost their lives and the Iraqi police and occupation soldiers were exposed as unable (and unwilling) to defend them - a breach of trust Sadr and the other Shia militias were swift to exploit. It was compounded by the wrangles over the interim Fundamental Law, which many Shia saw (via the so-called "Kurdish veto", where ten percent of Iraq's electorate can reject a constitution approved by 90 percent) as depriving them of the political power their history and numerical supremacy demands.
Both events highlighted the powerlessness of Shia religious and secular parties vis-à-vis the Americans. The US ferocious attack on Sadr - a decision taken without consulting the IGC which killed at a rate of 50 a day the very people the Americans claimed they had come to liberate - risked casting them as collaborators.
"We may get to a position where we can no longer defend our attitude in the eyes of our people," admitted Bayati. "The Shia has become progressively disappointed about the coalition's policies. We have tried our best to keep them calm. But if at the end of the day we can no longer convince our people, they will slip from our control. The Shias are the majority in Iraq. There are tribes with arms. They resisted the Baathist regime for decades. They cannot be controlled by force".
By taking the war to Sadr, the Americans have exposed the Iraqi face of their rule as the frailest of masks. In the Shia urban sprawl of Baghdad's Sadr City on 4 April, Mahdi fighters took over three of six Iraqi police stations to resist the incoming American tanks. The Iraqi police melted away. It was a flight repeated across the south. "What do you expect? The police have brothers in the Sadr movement - how could they fight them?" asks Habib Karim, a community worker in Sadr City.
By issuing a warrant for Sadr's arrest, the Americans closed the door on any political exit. The Mahdi swore to resist the move by all means. The Khoei family apparently dropped all charges against Sadr to avoid "bloodshed among the Shia and as an expression of Shia solidarity," Nithmi said. Three days after the warrant was issued the Americans - via the offices of Sadr's Dawa party -were in negotiation with the radical cleric to defuse a revolt they had created. The result was a sentence that could not be executed and another display of American weakness: unless the Americans decide to risk the bloodiest of contests in the Shias holiest of cities.
Will the two anti-occupation fronts evolve into one, united Iraqi resistance? Prior to the crisis, Sadr had reached out to Sunni Muslim movements, linking forces with groups like the Muslim Scholars Union (MSU) in demonstrations against the sectarian carnages in Karbala and Baghdad and the "divisive" Fundamental law.
That unity has deepened qualitatively in the current confrontation. There have been genuine displays of Sunni and Shia solidarity with the people of Falluja and reports of Sunni and Shia guerrillas traveling to each other's front lines.
There is also a nascent sense of a post-Baathist Iraqi identity, written in freshly daubed graffiti and embodied by the mass food and medicine collections stacked outside Sunni and Shia mosques. This plays down sectarian and historical divides in favour of a common Arab nationalism, Islam and anti-Americanism, all woven in the national-religious imagery of the Palestinian intifada. It is expressed by Mohammed Odeh, an 18-year old Mahdi fighter attending "common prayers" outside the main Sunni mosque in Baghdad: "I came to strengthen our religion and prove to the Americans we are one people".
But none of this amounts to a new Iraqi national movement or an anti-colonial revolt, according to Nithmi.
"Neither Sadr nor the resistance in Falluja will come under one leadership. He remains an individualist and they are fragmented into 20 different groups - and none have a discernable political program. But there is the possibility of an alliance between them, mediated by political bodies like the MSU and secular nationalist parties with Sunni and Shia cadre. This would not be a national movement but rather a national united front based on two demands: independence and an end to the occupation."
For now one thing is clear: whether through stupidity or ill thought out design, the Americans have provoked a reality their entire project in Iraq was designed to suppress: a revolt that expresses Iraqis' common Arab and Muslim identity.