The rise of ISIS, explained in 6 minutes

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.