EU Security Commissioner Julian King has a warning for European governments:  expect jihadists to come among those flying from the fall of Mosul.  The influx is “a serious threat that we must prepare ourselves for,” according to King, who trained in international security and then spent much of his career as a United Kingdom diplomat dealing with Ireland and Northern Ireland.

Of special concern to him were the 2,500 Islamic State (ISIS) fighters who are estimated to have come from European nations to begin with, as they would have all the necessary documents to return without legal difficulty.  Should Mosul fall, some number of its defenders will likely slip back to Europe, and the history of the conflict suggests that they would then carry out terrorist attacks at home.  Hundreds of such fighters have already come back, dwarfing the European security agencies’ capacities to deal with the threat that they pose.  The figure may rise above a thousand according to some estimates of the number of actual ISIS soldiers who have returned to infiltrate Europe.

“I don’t want to talk the risk down,” King told the German newspaper Die Walt.  “Even a small number constitutes a threat.”

So far at least the battle for Mosul has been characterized by tough fighting, rather than flight before the advancing armies.

The intense fight for hamlets some 30 miles from the city suggested that the militants could fight for every inch outside the city, but also that they are unlikely to be able to hold on in the face of a coordinated advance and close air support from a U.S.-led coalition.

Residents who have recently fled the area and Iraqi officials with contacts inside Mosul say the Islamic State has been digging in for a fight, erecting concrete barricades and filling trenches full of oil that can be set on fire to slow advancing forces. The Islamic State claimed to have carried out 12 suicide attacks on the first day of the offensive, according to its affiliated news agency, Amaq. Jabbar Yawar, a spokesman for Kurdish peshmerga forces, said eight Kurdish soldiers were killed Monday and 16 injured.

The stiffness of the resistance may change once a strategic tipping point is reached by the advance, but perhaps not.  ISIS is descended in part from al Qaeda in Iraq, which fought to the knife in Fallujah in 2004.  Its other predecessor organization was Saddam’s Ba’athist military elite, who have provided the organization with a professional core that al Qaeda in Iraq lacked.

Western forces are playing a supporting role in this conflict, mostly providing special operations advisers and air support.  However, there have been commando raids against ISIS targets.  Recently, a British Special Air Service soldier killed an ISIS soldier with an axe during a raid aimed at rescuing slave girls held by the Islamic State.  The Islamic State practices the slavery of women, especially for sexual purposes, in accordance with its plain-language reading of sharia law.  They have managed to turn it into a major source of fundraising through the use of online auction houses that have expanded their slave trade outside of the region they occupy.  This abuse of women is a serious violation of Western values of human dignity and sexual equality, explaining why precious resources like special operations commandos would be risked in order to free these girls.