The battle to retake Mosul from the Islamic was a slow one. Iraqi and other allied forces moved in from the east, first clearing the half of the city east of the Tigris River before moving onto the more populous western half.

The Islamic State put up a block-by-block fight, hiding in the homes of Mosul residents, slowing the battle significantly. The prolonged fighting was unexpected and it had deadly consequences. As my colleagues wrote Sunday:

The conquest brings to a close the toughest battle yet in the Islamic State war, one that lasted far longer than anticipated. When the offensive was launched last October, U.S. officials were privately predicting a two-month fight, and expressed hope that mass civilian displacement and widespread destruction could be avoided.Instead, the battle lasted for nine months, longer than the siege of Stalingrad and longer than the final Allied push into Germany in World War ll. It has cost thousands of lives, uprooted hundreds of thousands of people and reduced vast stretches of the city to rubble.