Abu Musab al-Zarqawi founded al-Qaeda in Iraq in 2004 but wanted total sectarian war. Bin Laden disagreed. After Zarqawi died in 2006, al-Qaeda in Iraq continued but was decimated by 2008.

The organization never disappeared. It rebuilt in Syria, renamed itself ISIS in 2013, and declared a caliphate in 2014 with Abu Bakr al-Baghdadi as caliph. Baghdadi had been detained at Camp Bucca, where he met Ba'athist officers and other militants who became ISIS leadership.

After release, Baghdadi rose in al-Qaeda in Iraq. When the group was decimated, he remained patient. When Syria's civil war began, ISIS saw opportunity. By 2013, it controlled significant Syrian territory. By 2014, it was ready to strike Iraq.

The Iraqi military collapsed when ISIS attacked Mosul in June 2014. What distinguished ISIS was its ambition: it didn't just conduct terrorism; it built a state with courts, taxes, and services.

The organization thought defeated in 2008 returned stronger in 2014. The surge and Awakening had destroyed operational capability but not the organization. Leaders fled to Syria, rebuilt, and returned. Sectarian policies and American withdrawal alienated Sunnis who tolerated ISIS as the lesser evil.

The rise of ISIS represented strategic failure in Iraq.