In 2014, Islamist militants seized large parts of Syria and Iraq to establish a 'caliphate'.

Led by 'caliph' Abu Bakr al-Baghdadi, Islamic State attracted fighters and supporters from around the world.

During its reign of terror, IS committed unspeakable atrocities, destroyed priceless cultural heritage and made $billions from taxes and oil smuggling.

Eventually, after five years of bloody battles, local forces backed by world powers drove IS out of its territories, scattering its fighters.

Now the fear is that any of several small 'emirates' in North Africa and the Middle East could expand to fill the void, with jihadist groups in Syria, Libya, Yemen and Mali best poised to build a new caliphate.

In north-east Syria's Idlib province, al-Qaeda breakaway group Hayat Tahrir al-Sham (HTS) has emerged as the dominant force:

HTS is quietly taking over the administration of the province, imposing a harsh interpretation of Islamic law... and enacting 'taxes' on aid convoys. ... HTS has more than 10,000 fighters, and may be able to recruit more from other groups.

Meanwhile, many Islamic State fighters are heading for Libya to join forces with warlord Khalifa Haftar; in Yemen, Al-Qaeda in the Arabian Peninsula (AQAP) has taken control of areas to the south; and in Mali, the Group to Support Islam and Muslims (called JNIM) grows increasingly powerful.