The Middle Eastern-based Islamic State (IS) goes by many names, such as the Islamic State of Iraq and the Levant (ISIL) or the Islamic State of Iraq and al-Sham (ISIS), but these are only recent denominations for an organization whose origins predate al-Qaeda's presence in Iraq. The forerunner of IS began as Jama'at al-Tawhid wa-l-Jihad, meaning "the Group of Monotheism and Jihad." Some sources claim [PDF] the organization's roots stretch back to 1999 while others place its origins in the turmoil that followed the US-led invasion of Iraq in 2001. Its founder, a Jordanian named Abu Musab al-Zarqawi, though originally refusing to join with Osama bin Laden's al-Qaeda organization, eventually assented to mutual cooperation. The two groups merged in 2004, following the agreement to form al-Qaeda in Iraq (AIQ). Al-Zarqawi was killed during a US airstrike in 2006. Following his death, his successors faced the Sunni Awakening, a counteroffensive of Iraqi Sunni tribesmen, backed by the US, rallying against the crimes of AIQ. The rift between al-Qaeda and the followers of the late al-Zarqawi began to surface after his death, as the faction that would later become IS began to call itself the Islamic State of Iraq (ISI).
In 2010, Abu Bakr al-Baghdadi, a tenured member of AIQ, became the leader of the organization. Baghdadi, like his predecessor, engaged in terrorism, mass killings and enslavement of women, among other crimes, all directed against the Shiite-dominated population of Iraq. The al-Qaeda leadership, under bin Laden's successor, Zawahiri, began criticizing the brutal conduct of Baghdadi and his followers. Then, in April 2013, Baghdadi and his followers broke away from al-Qaeda and adopted the name for which they are now known: IS. The creation of IS coincided with an extension of the organization's domain into Syria. In the wake of their new emergence, crimes allegedly committed by IS militants increased; 2013 was the bloodiest year in IS-controlled areas of Iraq and Syria since 2008.
Al-Qaeda, known throughout the late 1990s up through the early 2000s as a preeminent worldwide terrorist group, now denounces the actions of IS as extreme. By June 2014 IS had overrun the Iraqi army in major conflicts, and had come to control most of Iraq, from Mosul to Baghdad. Just how much territory currently under IS control is a matter of dispute. While exact estimates of total civilians under the dominion of ISIS are hard to calculate, BBC estimates the number at eight million people spread over five major cities. IS, in seeking to extend its influence further into Syria and over the portions of Iraq not already under its control, continues to commit mass executions and other human rights violations.