AP Explains: Iraq's slow grind to retake IS-held Mosul

BAGHDAD (AP) — Iraq's fight to retake Mosul from the Islamic State group has been the largest and the longest operation against the extremists in the nearly three years since they overran a third of the country. Mosul is Iraq's second-largest city after the capital Baghdad and was a key logistical and economic hub for IS when the extremists' footprint spanned much of Iraq's north and into neighboring Syria. Iraq's prime minister had originally pledged Mosul would be retaken by the end of 2