"The offensive in northern and central Iraq led by the Sunni Islamist insurgent and terrorist group the Islamic State (IS, formerly ISIL/ISIS) has raised significant concerns for the United States and precipitated new U.S. military action in Iraq. U.S. concerns include a possible breakup of Iraq's political and territorial order; the establishment of a potential base for terrorist attacks in the region or even against the U.S. homeland; the potential for a humanitarian catastrophe; and direct threats to the approximately 5,000 U.S. personnel in Iraq. The crisis has raised several questions for U.S. policy because it represents the apparent unraveling of a seemingly stable and secure Iraq that was in place when U.S. combat troops departed Iraq at the end of 2011. The Islamic State offensive into Kurdish-controlled territory in early August has caused the United States to become reengaged militarily in Iraq. The Administration has said its intervention will remain limited and will not result in a deployment of U.S. ground troops back into Iraq. The Administration also has engaged in humanitarian air drops to members of minority communities in northern Iraq that fled the IS onslaught."
CRS Report for Congress, R43612
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html