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The ISIS setbacks began over a year ago, when the fighters were forced out of the northern Syrian Kurdish town of Kobani by local Kurdish forces backed by US-led airstrikes.
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.
In all of 2015, the militants lost 14 percent of their territory in Syria, according to IHS, an analysis group that monitors the conflict. In the past three months, they lost another eight percent, a sign that the erosion is accelerating. The IHS figure roughly matches an estimate of a 20 percent loss given this week by US Secretary of State John Kerry.
In February alone, the SDF said it captured 2,400 square kilometers (927 square miles) consisting of 315 villages including the IS stronghold of Shaddadeh, on the main road linking the Iraqi city of Mosul and the Syrian city of Raqqa, the de facto capital of the "caliphate." SDF spokesman Col. Talal Sillo said the command will meet soon to plan for another offensive in northern Syria.
In Iraq, ISIS territorial losses have been more gradual. Coalition airstrikes have cleared the way for ground forces to reclaim towns and cities from Sinjar in the country’s north to Ramadi in the west. The coalition estimates that between the launch of the air campaign in August 2014 and January 2016, IS has lost between 21,000-24,000 square kilometers (8,100-9,200 square miles), about 40% of the Iraqi territory it once held.
Calls for a stepped-up campaign intensified after ISIS claimed responsibility for the Nov. 13 Paris attacks that left 130 dead and the Oct. 31 downing of a Russian jetliner from the Egyptian beach resort of Sharm el-Sheikh, which killed all 224 on board.
Deadly attacks in Turkey by ISIS that killed scores of people also spurred Ankara to tighten its closure of the border, making it difficult for the extremists to cross into Syria.
In an effort to squeeze the group’s finances, coalition and Russian warplanes in Syria began increasingly targeting ISIS oil assets in November. ISIS has since had to cut salaries and benefits for fighters.
Last week, Iraqi, Syrian and US officials confirmed that prominent ISIS military leader Omar al-Shishani died of his wounds from a US airstrike in northeastern Syria earlier this month.
US special forces also recently captured the head of the ISIS unit researching chemical weapons in Iraq, and airstrikes have targeted the group's chemical weapons infrastructure.
“As bad things start to happen, the less motivated, less disciplined, less radical elements of the force break and run,” US Army Col. Steve Warren said. “We’re going to keep seeing this.”
The United States estimates that as of last month, ISIS fields 19,000 to 25,000 fighters in Iraq and Syria - down from an estimated 20,000 to 31,500 - a number that was based on intelligence reports from May to August 2014.
A US official said the decrease reflects the combined effects of battlefield deaths, desertions, internal disciplinary actions, recruiting shortfalls and difficulties that foreign fighters face traveling to Syria. Still, these developments do not necessarily make ISIS less of a threat.
