The extreme Islamist violence that swept through Iraq this week has its echoes in Nigeria, Kenya and the Maghreb lands of North Africa. It marks the final collapse of Western schemes to divide up the world, and the rebirth of the notion of a Muslim caliphate straddling several continents One of my oldest friends, a ­Canadian diplomat, was kidnapped while on a UN mission five years ago in the Sahel, that 7,000-kilometre swathe of Africa running from the Atlantic to the Indian Ocean, by al-Qaeda in the Islamic Maghreb (AQIM). Held for 130 days, he told when released a tale of chilling import. These fanatics, he said, will not rest until they have recreated the medieval caliphate extending an Islamic empire throughout the Sahel, into the Maghreb (many of AQIM’s officers are ­A