Under a stepped-up campaign of U.S.-led and Russian airstrikes, as well as ground assaults by multiple forces in each country, the jihadis are estimated to have lost about 40 percent of their territory in Iraq and more than 20 percent in Syria. At their highest point in the summer of 2014, the group had overrun nearly a third of each country, declaring a "caliphate" spanning from northwestern Syria to the outskirts of Baghdad.
"What we are witnessing is that Daesh are not as determined as they used to be," Lt. Col. Fares al-Bayoush, commander of a Syrian rebel faction, said, using an Arabic acronym to refer to IS. His 1,300-strong Fursan al-Haq Brigade has been fighting against IS and Syrian government forces for more than a year.
"Now there are members who surrender, there are some who defect. In the past they used to come blow themselves up," he said.
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Clint Watts, a fellow at the Foreign Policy Research Institute, said IS is experiencing a phenomenon he's witnessed in other extremist groups that begin to lose territory.
"You've seen more and more reports of defectors just broadly, and you've also seen more reports of internal killings of so-called spies," Watts said. "As they lose ground and retract you start to see these fractures emerge in the organization."
In December, the predominantly Kurdish U.S.-backed Syrian Democratic Forces , or SDF, under cover of intense coalition airstrikes seized the Tishrin Dam, which supplies much of northern Syria with electricity. In the weeks that followed the forces gained control of more areas.