The saga of Iraq is, as an analyst put it, "a rather straightforward but sad story" since the U.S. military left the country at the end of 2011, only to find itself returning in a smaller way.
Some politicians feel the U.S. withdrawal of troops was a mistake, though public opinion favored it then.
Iraq's problems are bigger than Ramadi: its second largest city, Mosul, is now ISIS' capital, and Iraq still struggles with self-governance, politically and militarily.
Here are events since late 2011 that help explain Iraq's ongoing conflict:
U.S. troop withdrawal
December 31, 2011
After almost 4,500 Americans were killed and more than 30,000 injured since 2003 when the United States invaded Iraq, President Barack Obama orders the withdrawal of all troops.
The President welcomes them home.
"The war in Iraq will soon belong to history," Obama says. "Your service belongs to the ages.
"We are leaving behind a sovereign, stable and self-reliant Iraq, with a representative government that was elected by its people," the President also says.
The return of U.S. soldiers fulfills Obama's campaign pledge in 2008 to end the war.
In Iraq, the day is celebrated as "Iraq Day."
Tension grows between Iraq's Shiite and Sunni sects.
Their blood feud reaches back decades.
The Shiites control the central government under Prime Minister Nuri al-Maliki, and Sunni Vice President Tariq al-Hashimi is accused of terrorism by the top judicial committee. The body alleges al-Hashimi's security detail carried out 150 attacks between 2005 and 2011.
Al-Hashimi dismisses the accusations as politics,
noting the judicial committee is controlled by Shiites, and his party threatens to boycott parliament.
Killings hit a low
Some good news, relatively speaking.
Violence kills 112 people,
the lowest monthly death toll since the U.S-led invasion in 2003, officials say.
It's a good sign for the country's ability to maintain security.
Iraq also hosts an Arab League summit, a gathering that signals the political emergence of postwar democratic Iraq.
But it doesn't last long: By July, violence reaches a nearly two-year peak, with 325 deaths that month.
Backlash to Prime Minister and his Shiite-led government
Prime Minister al-Maliki comes under increasing criticism but he survives the threat of a no-confidence vote
President Jalal Talabani
announces that there is not enough support for the vote.
Al-Maliki's opponents accuse him of monopolizing power.
Later, Osama al-Nujaifi, speaker of parliament, presses efforts to oust al-Maliki and says the Prime Minister will be asked to appear before the governing body.
Sunni leader goes into exile
September 10, 2012
Al-Hashimi, Iraq's top Sunni politician, is given a death sentence in absentia, and he lashes out at the country's top Shiite leader, Prime Minister al-Maliki.
"The verdict is unjust, political and illegitimate and I will not acknowledge it," al-Hashimi tells reporters in Ankara, Turkey, where he has been living since fleeing Iraq five months earlier.
"To my dear people, I say, make sure that al-Maliki and those who stand behind him don't get what he wishes. Because they want sectarian strife," al-Hashimi says.
He remains in exile.
One year after U.S. withdrawal
December 31, 2012
The anniversary of the U.S. troops' departure is celebrated as "Day of Sovereignty."
But the political climate remains divisive.
Days before the anniversary, thousands of Sunnis protest in the streets of Anbar province, a region key to trade with Jordan and Syria, and the Sunnis denounced al-Maliki's order to arrest the bodyguards of Finance Minister Rafaie Esawi, a Sunni.
Sunnis and ethnic Kurds accuse al-Maliki and his Shiite political party
of cutting them out of the political process, an allegation that comes as U.S. lawmakers raise concerns about Iraq strengthening its ties with Shiite-dominated Iran.
Signs of ISIS rising
Concern looms that Sunni militants on both sides of the border will be capable of challenging governments in both Damascus and Baghdad and control a no-man's land.
This foreshadows the rise of ISIS,
which began as a splinter group of al Qaeda. The Islamic State in Iraq and Syria dreams of creating an Islamic state, or caliphate, across the Sunni areas of Iraq and in Syria.
The month also marks the 10th anniversary of the U.S.-led coalition invading Iraq and later ousting authoritarian leader Saddam Hussein.
Killings peak again
Iraq sees the deadliest month in the last five years since sectarian violence peaked in 2006 and 2007: 1,057 Iraqis are killed and 2,326 more are wounded in acts of terrorism and violence.
Al Qaeda in Iraq was declared "on the run" before the U.S. pullout, but now it and other Sunni extremist groups grow stronger
as the Shiite-led government fails to bring Sunnis into the political fold. Iraq's Sunni population claims that it is targeted by government forces and grows more alienated and disenfranchised.
Al Qaeda in Iraq has expanded into Syria under the umbrella of "Al Qaeda in Iraq and the Levant (Syria)."
Region's 'most dangerous players'
ISIS grows. It was known as al Qaeda in Iraq, but now the acronym "ISIS" appears more in news accounts as the militant group seeks to create a single Islamic state in Syria, Iraq and even Lebanon.
ISIS continues to exploit a security vacuum across Iraq. It and government troops battle in Ramadi and Falluja -- famous battlegrounds from the days when U.S. forces occupied the country.
U.S. Secretary of State John Kerry says the United States will help the Iraqi government in the battle against al Qaeda-linked fighters in western Iraq, but he stresses that America won't send troops.
ISIS fighters are "the most dangerous players in the region," Kerry says.
ISIS splits from al Qaeda
Al Qaeda and ISIS divorce, so to speak.
Al Qaeda's central leadership says ISIS "is not a branch of the al Qaeda group."
ISIS rejects al Qaeda's leadership.
One thing is clear: the jihadists are infighting.
Mosul falls to ISIS
ISIS seizes Mosul in northern Iraq
and threatens a march on Baghdad. Another northern city, Samarra, is besieged.
The speed of Iraq's deterioration surprises U.S. officials.
U.S. airstrikes begin
Obama authorizes "targeted airstrikes"
against ISIS outposts in northern Iraq as the militants advance to Irbil, known as a regional capital for the country's ethnic Kurds.
About 130 Marines and special operations forces are sent to northern Iraq to help tens of thousands
of the minority Yazidi people trapped in the mountains by ISIS, who vow to kill them. "Very specifically, this is not a combat boots on the ground operation," U.S. Defense Secretary Chuck Hagel says.
ISIS is "a credible alternative to al Qaeda,"
a U.S. intelligence official tells CNN.
ISIS shocks the world by releasing its first beheading video
of an American -- the victim is journalist James Foley -- and threatens the life of another American captive if Obama doesn't end military operations in Iraq. Other beheading videos will follow later.
Meanwhile, Prime Minister al-Maliki withdraws his candidacy
for a third term as pressure mounts abroad and at home for him to step down.
Replacing him will be Haider al-Abadi,
who, like al-Maliki, is a member of the Islamic Dawa Party, one of the country's biggest Shiite political blocs.
'This is going to go on'
Obama announces the United States will launch airstrikes against ISIS targets in Syria, too.
The United States underestimated ISIS
and overestimated the Iraqis' military will to fight, Obama says.
U.S. Secretary of State Kerry adds the expanded military campaign will take time to degrade ISIS.
"There's definitely a second day and there will be a third and more. This is going to go on," Kerry says.
Several other countries will join
the U.S. airstrikes against ISIS in Iraq and Syria.
Obama asks Congress for an OK
Obama asks Congress to formally authorize the use of the U.S. military
in the war against ISIS, but he doesn't call for ground troops in Iraq or Syria.
A victory for Iraqi military
Iraqi forces, joined by Shiite militiamen, enjoy a victory: They retake the city of Tikrit from ISIS.
Just a long commute from Baghdad
May 17, 2015
ISIS scores a victory whose symbolism resonates with Americans: After months of clashes with Iraqi and allied forces, ISIS takes control of the key Iraqi city of Ramadi
after government security forces pull out of a military base on the west side.
Ramadi is 70 miles west of Baghdad.