Islamic State (IS, also known as ISIS) has clearly weakened in the past year, according to the London-based International Institute of Strategic Studies (IISS). According to Emile Hokayem, senior fellow for the Middle East at IISS, IS has lost strength in terms of arms, territory and the flow of foreign fighters. But it still poses a threat, according to the latest Strategic Survey published by the organisation.

“ISIS is less defending clear state lines and more a guerrilla movement...