Jihadist banners flying. Victorious extremists on camera slapping and then executing dehydrated and pleading Shia members of the Iraqi security forces. Dark reports of mass slaughter. City charters released in captured territory heralding the implementation of an extreme version of Islamic law. We’ve seen it all before, but it remains shocking — and the latest advance by the Islamic State of Iraq and al-Sham (ISIS) is arguably the most disturbing development in Iraq’s already horrifying recent history.