What Is Isis and What Are Its Aims?

Isis, the Islamic State in Iraq and Syria, is a militant group so hardline that it was disavowed by al-Qaida. Recent photos and video appear to show members executing prisoners near Tikrit. Three years of civil war in Syria – and a manifesto that disavows notions of statehood and national boundaries – have helped it to claim hundreds of square miles of territory, and now it is gaining a foothold in Iraq, explains the Guardian's assistant foreign editor, Phoebe Greenwood