The Islamic State of Iraq and Syria is a phenomenon so terrible and shocking it seems impossible.
It controls an area the size of the United Kingdom, commits mass atrocities, and launches
terror attacks abroad.
To understand ISIS, it helps to tell the story of its rise.
That story begins far away and many years before ISIS existed.
In 1979 the Soviet Union invades Afghanistan to defend a puppet dictator against rebels.
Young men from the MidEast flock to join the rebels.
Many see it as a religious struggle, and some develop extremist views.
Among them is a well-educated young Saudi named Osama bin Laden.
Also in Afghanistan is a semi-literate former street thug from Jordan named Abu Musab Zarqawi.
They do not get along, and never will, but will create the groups we today know as al-Qaeda
and as ISIS.
The Soviets withdraw in 1989 and the Arab fighters return home.
Bin Laden grows al-Qaeda into a global network, to continue the struggle against Islam's enemies.
Zarqawi forms his own group, but it fizzles.
Both men later return to Afghanistan, now ruled by the Taliban.
On September 11, 2001, al-Qaeda attacks America from its base there.
The US invades Afghanistan and bin Laden flees to Pakistan.
Zarqawi, still obscure, flees to a remote and lawless corner of Iraq.
Two years later, the US does something that will transform the Middle East and set the
stage for ISIS: it invades Iraq.
The Americans topple Saddam Hussein's secular, Sunni dictatorship and disbands the Iraqi
army.
Thousands of Sunni Iraqi soldiers, angry and unemployed, join the insurgency.
Jihadist groups, also Sunni, see this as a repeat of the Soviet invasion of Afghanistan,
and again flood in to fight.
Zarqawi is among them.
Zarqawi's group becomes Iraq's most ruthless.
He especially attacks Shia, Iraq's majority, deliberately sparking a Sunni-Shia civil war.
By 2004, Zarqawi is a jihadist superstar.
Al-Qaeda, isolated and weakened, attempts to bolster its image by forming an alliance
with Zarqawi's group, which becomes known as al-Qaeda in Iraq.
But in 2006, Iraq's Sunnis rise up against Zarqawi, and the US kills him in an air strike.
Over the next few years al-Qaeda in Iraq is largely defeated.
The Americans withdraw in 2011 from an Iraq that finally looks stable.
In 2011, the Arab Spring spreads across the Middle East.
In Syria, Bashar al-Assad cracks down violently on protesters.
They eventually fire back, leading to civil war.
Assad fears the world will intervene against him.
So he releases jihadists en masse from Syrian prisons, tinging the rebels with extremism
and making it harder for foreigners to back them.
Back in Iraq, what little remains of Zarqawi's group is still allied with al-Qaeda but now
known as the Islamic State in Iraq.
It's led by a bookish religious scholar who calls himself Abu Bakr al-Baghdadi.
In early 2012, Baghdadi sends a top deputy to Syria to start a new al-Qaeda branch to
fight alongside the rebels: Jabhat al-Nusra.
Baghdadi also attacks a series of prisons in Iraq.
They free former jihadists and recruit new ones, growing stronger.
In April 2013, Baghdadi announces he is taking control of all al-Qaeda-allied forces in Syria
and Iraq.
His group expands into Syria, becoming the Islamic State of Iraq and Syria, or ISIS.
Al-Qaeda rejects Baghdadi's power grab and, in 2014, formally exiles him.
The two jihadist groups, long at odds, are now at war.
ISIS grows powerful in Syria, in part because Assad tolerates its rise, which he does because
it divides his enemies within Syria, and foreign powers are too focused on ISIS now to worry
about Assad.
By June 2014, ISIS has built an army in Syria, and it launches a military-style invasion
into Iraq.
The Iraqi army, weakened by corruption, folds with little fight.
Many Sunnis are tired of their Shia-dominated and increasingly authoritarian government,
and welcome or at least tolerate ISIS's arrival.
Within days, ISIS controls a third of Iraq and a big part of Syria.
ISIS's goal is more audacious than anything imagined by al-Qaeda: to revive the ancient
Caliphate and expand it to encompass all Muslims.
It earnestly believes its holy war will then bring about the apocalypse as foretold in
scripture.
Thousands of Muslims, mostly from the Middle East and from Europe, flock to join the group.
Some join for religious reasons, but many are just disillusioned or angry, and feel
that ISIS offers them answers and a purpose.
ISIS quickly overreaches.
That August, it invades Kurdish territory in Iraq and Syria, sparking counter-attacks
from better-organized Kurdish forces.
It launches a genocide against Iraqi Yazidis and murders the American journalist James
Foley on camera, outraging the world and provoking an American-led air campaign against it.
ISIS is unable to withstand the onslaught, and loses more than a fifth of its territory.
In response, it begins launching increasingly spectacular terror attacks abroad: Kuwait
City, Sinai, Beirut, Sousse and then Paris.
So-called lone wolves inspired by ISIS propaganda also launch attacks, though they're often
amateurish and less effective.
Eventually, ISIS will lose its state.
It is simply too weak, has no allies or outside funders, and is surrounded by enemies.
But ISIS will respond by reverting to what it was before, as AQI: an insurgency and a
terror group still capable of horrifying violence.
In that form, it could be around for years.