Updated

Iraqis head to the polls this weekend for the first time since the government declared victory against the Islamic State group, in national elections that could tilt the balance of power between the United States and Iran.

The May 12 election, the fourth since the 2003 U.S.-led invasion that toppled Saddam Hussein, will be dominated by the same leaders and factions that emerged 15 years ago. But the atrocities committed by IS against fellow Sunnis, the hard-fought national campaign against the extremist group and new rifts among the dominant Shiite blocs seem to have eased the sectarian tensions that marked past votes.

The main fault-line is between Prime Minister Haider al-Abadi, who has deftly balanced both Iranian and American influence, and other Shiite politicians seen as closer to Iran. The vote is being held amid rising tensions between Washington and Tehran, as President Donald Trump weighs withdrawing the U.S. from the 2015 nuclear deal, and Israel and Gulf countries express growing concern about Iran's regional ambitions.

Iraqis, meanwhile, expect little from what is sure to be another fractious coalition government. Fifteen years after the U.S. invasion, the country still suffers from widespread power outages and poor public services, and low oil prices have further eviscerated the economy. In Sunni-majority areas, where the war against IS destroyed vital infrastructure and countless homes, the challenges are even greater.

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THE CONTENDERS

Nearly 7,000 candidates are vying for 329 parliament seats. No single alliance appears capable of winning a majority, so the eventual government will be formed after horse-trading that could drag on for months. After the elections in 2010, it took eight months to form a new government.

The candidates leading the most powerful alliances are al-Abadi, former Prime Minister Nuri al-Maliki and Hadi al-Amiri, a former minister of transport who also led paramilitary fighters against IS.

Al-Abadi, who assumed office shortly after IS swept across much of northern and western Iraq, presided over the campaign that eventually drove the group from virtually all the territory it once controlled. He's seen as an urbane technocrat who has maintained good relations with Washington and Tehran. He also appears best placed to reach beyond the country's Shiite majority and court Sunni votes, which could provide a margin of victory in a close-fought race.

Al-Maliki, who governed Iraq for eight years, remains a powerful figure despite having stepped aside in disgrace when the military crumbled in the face of IS. His sectarian rule was widely seen as having fueled the rise of the extremist group. Al-Amiri was a commander in the Popular Mobilization Forces, the state-sanctioned and mostly Shiite militias who helped roll back IS. Both have close ties to Iran.

As with previous elections, Shiite cleric Muqtada al-Sadr, who also commands a state-sanctioned militia, is expected to translate his popular following into enough votes to make him a key player during government formation negotiations. His fighters once battled American troops, and he remains opposed to any U.S. presence in Iraq. But he's also seen as a nationalist leader who has at times clashed with Iran, and who has sought to improve ties with Iraq's U.S.-allied Gulf neighbors.

Iraq's complicated coalition politics also lend themselves to dark horses — both al-Abadi and al-Maliki were virtually unknown before they assumed office.

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THE U.S. VERSUS IRAN

The U.S.-led coalition played a key role in the defeat of IS. But since al-Abadi declared victory over the group last year, there have been mounting calls for the U.S. to withdraw. At a recent protest in Baghdad, hundreds of al-Sadr's followers gathered to protest, with many carrying signs calling the U.S. "the oppressor."

Some 5,200 U.S. troops remain in Iraq, according to figures released by the Pentagon in December. Al-Abadi has said he is open to a lasting U.S. presence focused on training Iraq's military. Many other Iraqis see the American forces as a bulwark against Iranian influence, and say the U.S. withdrawal of all troops in 2011 left the country vulnerable to the IS onslaught.

Iran also provided key support to Iraqi forces, particularly in the immediate aftermath of the IS blitz, when Iran-backed Shiite militias mobilized to defend Baghdad and halt the extremists' advance. Iranian influence has steadily grown since the 2003 invasion, and Iraq now occupies a central place in Tehran's regional strategy, linking Iran to allied forces in Syria and Lebanon.

It's unlikely any elected Iraqi government would be hostile to Iran, but most Iraqis are deeply nationalistic and may prefer al-Abadi's centrist approach. The country's top Shiite cleric, Grand Ayatollah Ali al-Sistani, has warned against foreign interference in the upcoming vote.

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WANING SECTARIANISM

The Sunni-Shiite divide in Iraq, which fueled much of the violence after 2003 and paved the way for the rise of IS, appears to have waned in recent years, as Sunnis both suffered under the extremists' brutal rule and paid a staggering price for their defeat.

More than 2 million Iraqis were displaced by the war against IS, mainly from Sunni areas, where the fighting left entire towns and neighborhoods in ruins. Sunnis remain deeply divided, and the various Sunni parties are unlikely to expand their limited presence in parliament.

But rather than boycott the vote, as they did in some past elections, Sunnis appear more interested in partnering with Shiites. Shiite politicians are campaigning in Sunni-dominated areas for the first time, and al-Abadi has welcomed Sunnis to his alliance.

Iraq's other sizeable minority, the Kurds, are deeply divided following last year's independence referendum, which was rejected by Iraq and its neighbors, and which prompted Baghdad to seize long-disputed areas from Kurdish forces. Masoud Barzani, who heads one of the two main Kurdish factions and who orchestrated the referendum, now faces heavy opposition. The resulting split could make it difficult for the Kurds to act as a swing vote when it comes time to form a coalition government.

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CHALLENGES AHEAD

The vote is unlikely to change Iraq's entrenched political system, which since 2003 has failed to deliver basic services to its citizens. "You are not going to see a new political class," said Kirk Sowell, the publisher of Inside Iraqi Politics, a political and security newsletter.

With a GDP of over $170 billion, Iraq is considered an upper-middle income country by the World Bank. But most Iraqis receive just a few hours of electricity a day, tap water is undrinkable and the health care system is in ruins. Ministries have long been divvied up among the various political factions in return for their support, resulting cronyism and ineptitude.

"I swear, nothing will change. I am telling you, it's a garbage recycling facility. Just like in 2006, 2010 (and) 2014," said Ali al-Khafaji, a Baghdad resident. "It's the same parties that have destroyed Iraq."

Iraq struggled to provide services even when oil was more than $100 a barrel, and even before the war with IS left it with a reconstruction bill estimated at $88 billion. Oil prices have gradually inched up in recent months, and the government raised $30 billion in loans and pledges at a conference in Kuwait late last year. But the U.S. has said Iraq must attract private investment, a tall order given the widespread destruction of infrastructure and lingering security issues.

Although it no longer controls pockets of territory, IS has continued to stage insurgent-style attacks, and has threatened to target the elections themselves. The extremist group is widely reviled, even in Iraq's Sunni heartland. But it has risen from the ashes before, in part because of widespread grievances that the upcoming elections are unlikely to address.

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Associated Press writers Ahmed Sami in Baghdad and Salar Salim in Irbil, Iraq, contributed to this report.