Nearly two years ago, a relatively obscure Islamic militant group with loose ties to al Qaeda announced a reorganization and name change to reflect its goal of creating a caliphate in Iraq and Syria.
From that point in April 2013, it was known as ISIS, for Islamic State in Iraq and al-Sham. Taking advantage of power vacuums in war-torn Iraq and Syria, the group positioned itself as a legitimate force. But it would be many months before its march of destruction would gain worldwide notoriety.
Initially, ISIS seemed to pursue a two-pronged offensive: fight the Syrian government for control of key territory, including along the Turkish border, and seize strategic areas of Iraq. That approach bore fruit in the summer of 2014, with the fall of several Iraqi cities, the capture of the country's largest dam and attacks on a large oil refinery and an air force base. In Syria, ISIS captured another oil field, and engaged government forces in a two-week battle at an air force base. The group also expanded into Lebanon.
In August, the United States announced airstrikes against ISIS in Iraq, primarily to stop an expected slaughter of religious minorities trapped on a mountain. Later that month, ISIS beheaded an American for the first time — James Foley, a photojournalist. Another American, Steven Sotloff, was killed shortly after that, part of a series of beheadings of Westerners.
U.S. and allied airstrikes expanded to Syria in September, including against ISIS targets in Kobani, on the border with Turkey. ISIS was driven from that city but made other gains — including the capture of a gas field in Homs, Syria, and its first victory in Libya, another country ravaged by civil war.
In February, ISIS beheaded two Japanese hostages and released a videotape of a captured Jordanian pilot being burned alive. Jordan responded with airstrikes on ISIS in Syria. The day after, on Feb. 6, ISIS claimed a strike had killed its last American hostage, aid worker Kayla Mueller. The following week, ISIS released a videotape showing the execution of 21 Coptic Christians in Libya. Egypt launched retaliatory airstrikes against ISIS in Libya.
The conflict has continued to escalate, with reports of ISIS militants kidnapping Christians from villages in northeastern Syria, and Pentagon officials describing plans by the Iraqi military to try to retake the city of Mosul in April.
And ISIS' numbers continue to grow. CIA estimated that ISIS had 4,000 fighters in Iraq alone in June 2014. By September 2014 that estimate was increased to between 20,000 and 31,500. Today, other countries estimate ISIS has 200,000 fighters in the entire region.