BAGHDAD — The extremists of the Islamic State appeared unstoppable after their sudden blitz through Iraq this summer, with its battle-hardened fighters continually raising their black flag over newly conquered areas.

Today, roughly a third of Iraq is dotted by active battle fronts, with intense fighting and occasional Islamic State victories. But analysts also say the days of easy and rapid gains for the jihadists may be coming to a close in Iraq, as the group’s momentum appears to be stalling.

The international airstrike campaign against the Islamic State, also known as ISIS or ISIL, has clearly played a role in slowing the Sunni Muslim group’s advance. But analysts say other factors are having a major effect, including unfavorable sectarian and political demographics, pushback from overrun communities, damage to the group’s financial base in Syria and slight improvements by ground forces in Iraq.

Across the territories the Islamic State holds, the group has overhauled its operations. Bases and hospitals have been evacuated and moved to civilian homes that are harder to identify and bomb, Iraqi officials said. Fighters who used to cross the desert in convoys now move in small groups or by motorcycle.