Using Mosul as a base, the jihadi group swept further south through Iraq's towns and cities, but government soldiers trained by U.S. forces have since gained ground and Mosul is now the last city in the country held by IS.
The UN has expressed "extreme concern" for the safety of up to 1.5 million people in the area.
The U.S.is now providing air cover as Iraqi security forces and members of the Kurdish militia begin their attempt to retake the city over the next several weeks.
If the Islamic State's capture of Mosul marked the high point of the group's expansion, its expulsion would mark a major setback for a group that's steadily been losing territory in Iraq and Syria. "God willing, we shall win".
If successful, the liberation of Mosul would be the biggest blow yet to the Islamic State.
In Washington, Defense Secretary Ash Carter called the launch of the Mosul operation "a decisive moment in the campaign" to deliver a lasting defeat to IS.
The forces converging on Mosul wave a variety of flags, including the Kurdish regional flag and Shiite religious banners.
Most of the coalition's support has come in the shape of airstrikes and training, but US, French and British special forces are now also on the ground to advise local forces. Iraqi troops also deployed east of Mosul in the Khazer area, along with Kurdish peshmerga forces, and to the north of the city near the Mosul Dam and Bashiqa areas. But the battle for Mosul is likely to be long and at was unclear at this early stage when the troops would enter the city itself.
Since the official start of the US -led campaign against the Islamic State in Iraq and Syria in 2014, USA military officials have stressed that American troops would not be in a combat role, and instead relegated to "advising and assisting" their Iraqi counterparts from behind the front lines.
In addition to the seven strikes launched on October 8, the combined coalition air forces hit the city with four strikes on October 9, four strikes on October 10, four strikes on October 11, one strike on October 12, five strikes on October 13, and another strike on October 15. Iraqi government and Kurdish forces, backed. It was in Mosul's Great Mosque that Isis leader Abu Bakr al-Baghdadi announced his self-proclaimed caliphate more than two years ago.
British aircraft have been providing "intensive" support to Iraqi troops in the build-up to the Mosul operation and Sir Michael said the United Kingdom would continue to play a "leading role" in the fight against IS.
"But ultimately the decision to move forward with this operation is one that was made and should be made by the prime minister of Iraq", he said. The role of the Shiite militias has been particularly sensitive, as Nineveh is a majority Sunni province and Shiite militia forces have been accused of carrying out abuses against civilians in other operations in majority Sunni parts of Iraq. Mosul is about 360 kilometres (225 miles) northwest of the capital, Baghdad. The fighting is certain to drive out civilians, and the Iraqi government and aid groups are anxious about a humanitarian crisis.
He said: "We are calling on the UK Government to put pressure on the Iraqi and coalition forces around Mosul now to establish safe corridors, safe escape routes for children to get out". The Iraqi Government has told civilians to stay inside their homes so they aren't caught in the cross fire. "But the military has said that. we could see that within five to six days", she said.