The northern Iraqi city of Mosul is burning, as insurgents from an offshoot of al-Qaeda take control while Iraqi security forces leave behind their military uniforms and flee the region. It’s an ugly situation, and it’s unlikely to turn around soon, said a former senior U.S. military commander in Iraq. Here’s why:

1) The insurgents have the momentum. The situation is even more serious than most people in the United States realize, the former U.S. commander said. In capturing parts of Mosul, the insurgents have captured Iraq’s second-largest city, likely giving them additional resources to use in their fight against the central government in Baghdad. That could include money, arms and ammunition. 

“When a force like that gets momentum and the security forces start to crumble, it becomes difficult to stop,” said the former U.S. commander in Iraq.

2) The insurgents’ group could be growing. The force that took over Mosul on Tuesday is affiliated with the Islamic State of Iraq and Syria. The group formed in the months following the U.S. invasion of Iraq in 2003. The group was once affiliated with al-Qaeda, but they split early this year in part because ISIS is even more extreme. Beheadings, floggings and other punishments the organization has dished out in Syria led to a revolt in the northern part of that country, in which another al-Qaeda affiliate, Jabhat al-Nusra, fought ISIS alongside more moderate Syrian rebels.

The force that took over Mosul likely numbers in the hundreds, the former U.S. commander in Iraq said. It could be armed with weapons that fell into their hands after ISIS raided an arms depot in Syria that reportedly had been stocked with help from the CIA. The group is said to have freed hundreds of prisoners, at least some of whom could join the insurgency.

3) The insurgents are heading south toward Baghdad. Mosul, in Iraq’s northwestern corner, is some 220 miles from Baghdad. By Wednesday, they had already captured the cities of Tikrit, which is more than halfway to Baghdad from Mosul, as well as Baiji. The question becomes when and where Iraqi forces are able to stand their ground against the insurgent advance.

4) The Kurds in northern Iraq may seek to harden unofficial internal borders it keeps with the rest of the country. As The Washington Post’s World Views blog pointed out this afternoon, Iraq’s autonomous Kurdish government in northern Iraq has laid claims of its own upon Mosul, sparking concerns of a civil war between Kurdish forces and the Iraqi military. Now, the Iraqi military is in shambles, leaving the Kurds to figure out what to do next to protect themselves against ISIS.

5) More U.S. help will be limited in scope, and much of it won’t arrive for months. As noted on Checkpoint this morning, the United States has promised a variety of muscular weapons to Iraq in coming months. But that materiel won’t be arriving now, as the crisis in Iraq continues to erupt.

Asked about the situation, Adm. John Kirby, a Pentagon spokesman, said Tuesday that United States currently has a $14 billion foreign weapons program with Iraq in place. But he made it pretty clear that the United States won’t be offering new forms of military assistance any time soon.

“This,” he said, “is for the Iraqi security forces and the Iraqi government to deal with.”

This item was updated Wednesday to reflect new developments.