The Islamic fundamentalist group ISIS continued its rampages across Iraq on Saturday and captured several key towns in that country’s Western Anbar province, officials said. Security authorities told CNN this weekend that ISIS controls 70 percent of Anbar and had seized key towns which operate border crossings with Syria and Jordan.

Among the reasons why ISIS has been able to take over so much of the country in so little time is the Sunni population’s embrace of ISIS as that minority population welcomes an alternative to the exclusionary and repressive administration run by Iraqi Prime Minister Nouri al-Maliki. ISIS has, in turn, endeavored to fill the vacuum left by retreating Iraqi administrators by providing the services expected of a state.

Last week, the global affairs columnist Michael Weiss explained the lengths to which ISIS is going in order to create the impression that it is a state-like entity:

No one expects a marauding guerrilla group to adjudicate petty disputes between competing local leaders or to maintain failing local infrastructure, but they do expect that of a state. One report in the Emirates-based publication The National filed out of Iraq’s Nineveh Province suggests that ISIS is being stalled slightly by that ancient nemesis of all rampaging revolutionary armies: politics.

Ideological differences among the various militant groups who make up the ISIS coalition are beginning to put a serious strain on that army’s operational capability, The National reported.

The first signs of a split emerged on Saturday, with reports of fighting between the Islamic State of Iraq and the Levant (ISIL) and the Naqshbandi Army, formed by officers from the former dictator Saddam Hussein’s military, that left 17 people dead.

“[W]itnesses said the two sides clashed over who would take control of fuel tankers in the area,” the report read.

The ISIS alliance is supported primarily by Sunni tribal leaders and the former members of Saddam Hussein’s outlawed Ba’ath Party. While both these groups are hostile toward the al-Maliki’s Shiite dominated government in Baghdad, they “agree on little else,” The National report read.

“This friction may be compounded by public frustration over power outages and fuel shortages in captured territory,” it continued.

What’s more, ISIS may be alienating those locals who initially welcomed the militant group. “When ISIL first came to those areas, they seemed to be trying to reach out the local population,” said Bashar Mahmoud, the head of a provincial council in Mosul before that city fell to ISIS fighters. “But then they started killing members of these tribes and that has infuriated their leaders.”

If ISIS alienates both local tribal leaders and The Naqshbandi Army, the pro-Ba’athist force behind its early success in the North of Iraq, ISIS’s stunning early momentum may be stalling.