Ten years after the United States barreled into Iraq with extraordinary force and a perilous lack of foresight, the country is neither the failed state that seemed all but inevitable during the darkest days of the war nor the model democracy that the Americans set out to build.

Haunted by the ghosts of its brutal past, Iraq is teetering between progress and chaos, a country threatened by local and regional conflicts that could drag it back into the sustained bloodshed its citizens know so well.

The nation is no longer defined or notably influenced by its relationship with the United States, despite an investment of about $1.7 trillion and the loss of 4,487 American troops. In the end, Washington failed to carve out a role as an honest broker in postwar Iraq, an aspiration born out of the recognition that the country’s future may again have explosive implications for the region.

The contrasts of today’s Iraq are as sharp as they are dangerous. The autonomous Kurdish region in the north is thriving, inching ever closer to independence, buoyed by an oil boom and bold, ambitious leaders who have kept the area safe. The Shiite provinces in the south are enjoying a renaissance, reaping millions from improved security and the exponential growth of religious tourism.

(From March 20, 2003: Explosions rip through the quiet of morning)

2003 to 2013: A wide-angle look at Iraq

Predominantly Sunni areas, meanwhile, are seething. The minority, which enjoyed elite status under Saddam Hussein’s autocratic reign, views itself as increasingly disenfranchised in the Shiite-run state of Prime Minister Nouri al-Maliki; its members have resorted to large-scale protests in a bid to claim a fair share in the new Iraq.

Drawing on Sunnis’ widespread anger and frustration, remnants of Iraq’s once-mighty insurgency remain a threat, periodically striking at the heart of the state. On Tuesday, a series of bombs detonated in the capital, killing at least 48 people in predominantly Shiite neighborhoods. It was the deadliest spate of violence in Iraq so far this year.

Undercutting Iraq’s quest to regain a seminal position in the region are the politics of Baghdad, which have become more intractable and poisonous since the U.S. military withdrew at the end of 2011. They have widened Iraq’s ethnic and sectarian fault lines and called into question the viability of a parliamentary democracy in a country accustomed to strongman rule.

Pockets of the new Iraq are brimming with optimism. To drive around the southern province of Najaf, home to one of the most sacred shrines in Shiite Islam, is to behold the type of Iraq that the United States once hoped to leave behind.

Cranes are ubiquitous as a construction boom reshapes the provincial capital. Struggling to accommodate the more than 2 million pilgrims who annually visit the Imam Ali Mosque, the holy site is adding wings. Najaf’s streets are wallpapered with campaign posters for upcoming provincial elections.

“Most people now have a good job and lots of opportunities,” Gov. Adnan Zurfi said in a recent interview as he listed a flurry of initiatives the province is funding to improve health care, housing for the poor and education. Baghdad’s dysfunctional politics notwithstanding, he noted, democracy is thriving in Najaf.

“This is an example of a successful city,” added the governor, an Iraqi-born American citizen who spent several years in Dearborn, Mich. “I’m trying to show people in Iraq that there are a lot of benefits to the new system if they manage to elect good people and kick radicals out of power.”

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Haider Adnan, a 30-year-old merchant who sells fabric to pilgrims visiting the shrine, said business has never been better.

“The economy is good,” he said, as hordes of religious tourists made their way through the labyrinth-­like shopping arcade adjacent to the shrine. “We have jobs, trade — it’s the best it’s ever been.”

This side of Iraq stands out as an unlikely success story in a nation where an estimated 120,000 civilians were killed during the past decade.

Sunni angst

The new Iraq looks far bleaker in the predominantly Sunni regions in the west, the capital and provinces north of Baghdad — once the heart of the insurgency. Sunnis have seen their clout erode sharply over the past two years as they have gotten squeezed out of national politics and the government, by far the country’s leading employer.

As the last American troops were leaving Iraq in December 2011, Maliki’s security forces set out to arrest the country’s Sunni vice president, Tariq al-Hashimi, whom authorities had accused of running death squads. Hashimi barely managed to flee the country and has resettled in Turkey, prevented from returning home by a death sentence imposed after his conviction in absentia on terrorism charges.

This past December, security forces arrested bodyguards of another prominent Sunni politician, Rafia al-Issawi, on terrorism-related charges, forcing him to take refuge in his native Anbar province in the west. The case against the former finance minister set off a wave of protests across the country, raising the specter of an Arab Spring-like uprising.

Security forces have largely avoided clashing with the demonstrators, although they have killed a handful of protesters. Authorities have worked assiduously to stifle the movement in Baghdad, blocking access to Sunni neighborhoods on Fridays, when prayers and protests are held. This past Friday, Iraqi troops blocked traffic to the Adhamiyah neighborhood, one of the protest hubs.

“We are trying to show the world that people here are suffering from injustice,” said Mohamed al-Ani, 63, a resident of Adhamiyah who has joined the demonstrations. “If the government continues to prevent people from claiming their rights, the situation will boil over.”

Many in a community that had become largely resigned to its postwar fate are galvanized. Sunnis are calling for the repeal of an anti-terrorism law that the government has used to detain Sunnis en masse and for expanded employment opportunities.

In Arab provinces north of Baghdad, the situation is even more tense. In addition to Sunni protest movements that have taken root there, provincial officials and tribal leaders have become increasingly wary about an escalating dispute between Baghdad and the Kurdish region over a 300-mile swath of contested territories.

Last year, Maliki bolstered Baghdad’s military presence along the disputed territories, drawing protest from Kurdish officials, who have sought to expand their domain southward in recent years with the goal of fully controlling the oil-rich city of Kirkuk. The Kurds have responded to Maliki’s move in kind, resulting in an uneasy stalemate.

Tension between the Baghdad government and the Kurds has soared over plans to build a pipeline connecting Iraqi Kurdistan and Turkey — a step that would give the autonomous region greater independence from the central government and could pave the way for complete sovereignty.

The impasse led Maliki to warn in a recent speech about the likelihood of a new “ethnic conflict” that would be “unfortunate and painful.”

Wassfi al-Assi, a tribal leader in Kirkuk who has been active in the protests, said Sunni Arabs in the north are as unnerved as they are disillusioned, fearing that they will bear the brunt of any conflict.

“Iraq used to be one of the developed countries of the region,” he said. “Now we’re seen as a Third World country. There are many calls for dividing Iraq, even more than during the occupation time.”

Stoking tension

In nearby Nineveh province, which also borders the Kurdish region, disenchantment with the government and hardening sectarian and ethnic positions are bolstering the insurgency, said Abdullah al-Yawar, a powerful tribal leader.

Insurgent movements “grow when people feel that their lives are bad,” Yawar said, noting a recent string of attacks against candidates running for seats on the provincial council. “When people feel that the government humiliates them, those are the conditions under which they can work.”

Bombings and other attacks remain far less frequent than during the peak of the war, but violence has worsened in recent months, according to a new report on developments in Iraq by the U.N. mission here. Between mid-November and Jan. 31, 741 civilians and 311 members of the Iraqi security forces were killed, according to the report, which noted a rise in suicide and rocket attacks, as well as a resurgence of “mass casualty” strikes that aim to stoke sectarian tension.

One big bombing occurred Thursday in Baghdad. As Rabab al-Maliki, 45, was leaving her clerical job in parliament, walking between concrete blast walls, the first explosion thundered.

She dashed into a concrete bunker left behind by the U.S. military and braced for what has become routine: secondary blasts. Three more followed, making her shudder. Gunmen had bombed nearby government buildings, seeking to detonate explosives inside the most loathed one: the Justice Ministry. After the fourth blast, she hurried back to her office, frazzled.

The war, she said wryly, cost her her marriage. Maliki, a Shiite, was married to a Sunni man, but sectarian tension made the union unsustainable. More important, she said, it had robbed her of the will to live.

“I don’t care about anything,” she said, speaking in a cluttered, windowless office. “Your ambitions here are limited. You can’t be happy.”

Jabbar Yaseen contributed to this report.