The Islamic State of Iraq and Syria (ISIS) has emerged from radical Sunni jihadists in Iraq who fought under the banner “al-Qaeda in Iraq”.

Their goal since being founded in 2004 is to create a hardline Islamic state crossing over the borders of Syria and Iraq.

If they achieve their aim, the new state would be a caliphate led by a supreme religious leader called a caliph.

What is a caliphate?

Caliph means successor in Arabic, and a cleric with this title is regarded by Sunni followers as an Iman chosen by Allah from the Family of the House, direct descendants of the Prophet Muhammad.

One map drawn up by ISIS as early as 2006 shows a region similar to the territory it controls today in north-east Syria and northern Iraq.

The area, roughly the size of Belgium, contains many oil wells.

Another map from the same time targets a far larger area crossing into Jordan, Lebanon and Israel.

The single most important factor in ISIS's recent resurgence is the conflict between Iraqi Shias and Iraqi Sunnis.


What's the difference between Shias and Sunnis?

The majority of Iraqis – between 60% and 70% - are Shias.

However ex-dictator Saddam Hussein was a Sunni and the absolute power of his Ba'ath party gave Sunnis the belief that they are the real majority and legitimate rulers.

The difference between the two largest Muslim groups originated with a controversy over who got to take power after the Prophet Muhammad's death in 632AD.

Yasser Arafat is pictured meeting with Saddam Hussein
Legitimate rulers: Saddam Hussein was a Sunni

Abu Bakr was chosen as caliph, but a minority of Muslims favoured another man, Ali. Ali's followers became known as Shiat Ali, partisans of Ali – Shias.

In 656, Ali became the fourth caliph after Abu Bakr was assassinated. Some Muslims, the ancestors of today's Sunnis, rebelled against him.

Ali himself was assassinated in 661 after violence spread.

But what about the Western conflict in Iraq?

US troops and allied Sunni militias defeated al-Qaeda in Iraq during the post-2006 troop surge, however the surge did not destroy its fighters completely.

In 2010, the US commander in Iraq, General Ray Odierno, described the group as “fundamentally the same.”

In 2011, senior ISIS members regrouped following the freeing of high-profile members held by the Iraqi Government.

ISIS leader Abu Bakr al-Baghdadi was in custody at a US detention facility in Iraq until 2009 when he was handed over to the Iraqi authorities.

Abu Bakr al-Baghdadi
Leader: Abu Bakr al-Baghdadi is in charge of the group

As he left Camp Bucca, near Iraq's southern border with Kuwait, he told his captors: “I'll see you guys in New York.”

It has been claimed that al-Baghdadi, who uses a variety of aliases, was only radicalised while in US custody.

According to this story, he was a farmer wrongly swept up and became a follower of bin Laden at Camp Bucca.

However, it is more likely al-Baghdadi was an Islamic fundamentalist before the US and Britain invaded Iraq.

There are only two known photos of the 43-year-old al-Baghdadi, who Iraqi military officials believe is hiding somewhere in Iraq’s eastern Diyala province.

In 2012, sensing an opportunity, Baghdadi dispatched some foot soldiers to join the fighting against Bashar al-Assad’s government in Syria.

In 2013 he announced that the group was merging with Jabhat al-Nusra, the other al-Qaida affiliate in Syria, to form a new group called the Islamic State in Iraq and al-Sham.

Nusra, predominantly Syrian in membership, is more focused on the overthrow of Assad, whereas ISIS is more international and interested in expanding its territory and enforcing Shariah law.

In February this year al-Qaeda leader Ayman al-Zawahiri formerly dissociated the worldwide terror network from ISIS following its huge gains in Syria.

Extraordinarily, this was because al-Zawahiri, Osama bin-Laden's right-hand man at the time of the 9/11 New York attacks, felt his one-time proteges were responsible for too many civilian deaths.

Al-Qaeda does, however, recognise its jihadist affiliate Jabhat al-Nusra, regarded as less extreme, in Syria.