Much of the current violence is the work of hard-line Sunni jihadists of the Islamic State of Iraq and the Levant, or ISIL.
They've refined the tactic of multiple suicide bomber attacks and other relatively complex operations that have claimed more than 400 lives this month alone.
Most of the victims are Shiites. So far the Shiites have largely stayed their hand. But there are fears all-out sectarian war soon may erupt again.
"The violence in Iraq remains largely limited to attacks undertaken by small militant cells, while the general population continues to stay uninvolved and civilian-on-civilian ethno-sectarian violence is still relatively rare," Iraq expert Michael Knights said.
But, he stressed, the nearly two years of intensified al-Qaida mass-casualty attacks and sectarian massacres "are beginning to severely test Shiite patience, resulting in growing evidence of revenge attacks on Sunni mosques, preachers and civilians."
With parliamentary elections scheduled in 2014, and Prime Minister Nouri al-Maliki determined to remain in power at the head of his Shiite-dominated coalition, there's a danger the violence will escalate in the months ahead.
The tempo of the bloodletting rose sharply in April after Maliki, who since his election in 2006 has cemented control of the largely Shiite military and the almost exclusively Shiite security services, began a deadly crackdown on Sunnis protesting what they see as marginalization. Dozens were gunned down.
The United Nations said 712 people were killed in April. Since then the death toll has risen inexorably every month and continues to mount.
Since U.S. troops completed their withdrawal from Iraq in December 2011, Maliki has had to rely on his own U.S.-trained forces, which are widely seen as heavy-handed and inept.
Unlike the Americans, who eventually realized they had to win over the Sunnis if they wanted to beat al-Qaida, Maliki's government is not getting a flow of intelligence from Sunni tribal leaders who turned against al-Qaida. Instead, he is trying to eliminate them.
There has also been a surge in executions by Maliki's government under the country's draconian 2005 Anti-Terrorism Law, generally viewed as an attempt to intimidate his political opponents.
Amnesty International reported Oct. 10 that 41 men and one woman had been hanged in Iraqi prisons in a two-day period after what the human rights group described as "grossly unfair trials."
All told, 125 people have been executed this year, making Iraq one of the world's most prolific executioners after China and Iran.
Some 500 executions have been carried out since 2005, when the Shiite-led government reinstated the death penalty.
The war in Syria, which has allowed al-Qaida to greatly strengthen its power and influence, has accelerated the sectarian violence in Iraq, and whole units of jihadist fighters rotate between operations in the two countries.
ISIL's not the only militant Sunni group. The Army of the Men of the Naqshabandi Order, largely made up of former Saddam Hussein loyalists, is also active.
It is commanded by Izzat Ibrahim al-Douri, Saddam Hussein's former vice president and the last of Saddam's inner circle still at large. He has eluded capture or assassination since Saddam's regime was toppled in 2003.
But it's ISIL, the dominant militant organization in Iraq and Syria, that sets the tempo of terrorism.
Iraqi officials and security analysts say its strength, currently estimated at some 4,000 fighters, is increasing as its killing power expands. There seems to be no shortage of recruits for the multiple, highly choreographed suicide bombings that are its grim trademark.
The Long War Journal, which monitors global terrorist activity, reported Tuesday ISIL has used at least 25 suicide bombers in Iraq since Oct. 1.
Eight of them, in vehicles and on foot, took part in a complex assault Sunday on police and local government around the western town of Rawa, in Sunni-dominated Anbar province, a jihadist stronghold.
These operations are part of the "Destroying the Walls" offensive declared July 21, 2012, by al-Qaida's Iraqi emir, Abu Bakr al-Baghdadi, to destroy Maliki's security and governmental infrastructure.
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