Three days after the battle for Mosul was launched on Monday, efforts by Kurdish and Iraqi soldiers to retake the major city were slowed Wednesday by remotely detonated bombs, concrete barriers and booby traps. "It’s going to be a tough fight and a difficult fight," President Obama acknowledged Tuesday, as more signs of resistance emerged from the Islamic State stronghold.

Mosul is the largest city in northern Iraq, and more than 1 million residents are believed to remain there, amplifying fears of a humanitarian disaster in case of a prolonged battle in which Islamic State fighters might use civilians as human shields.

"Every minute passes like a year," a father of three trapped in Mosul was quoted as saying by the Associated Press.

But the battle for the city could last for months, as did the liberation of the city of Ramadi from the Islamic State, a.k.a. ISIS, in central Iraq. The most intense fighting there occurred between November 2015 and January 2016.

Residents paid a heavy toll for the liberation of Ramadi, the capital of Anbar province. According to a satellite imagery-analysis by several U.N. agencies, nearly 2,000 buildings, streets or bridges, among other structures, were destroyed between July 2014 and end of January 2016, when most fighting had ended.

By the time ISIS was finally forced out of Ramadi at the beginning of this year, large parts of the city had already been reduced to rubble. Satellite images released in May show what victory over ISIS looked like for Ramadi back then, and they are a strong reminder of the possible consequences Mosul faces if the battle drags on.

Iraqi governmental and Kurdish forces are still miles away from Mosul, but the efforts to reach the city will leave behind a path of destruction. In Ramadi's case, the fighting destroyed a highway bridge overpass — an important infrastructure junction.

Even harder hit were Ramadi's inner districts. Haji Ziad square used to be a vibrant part of the central Iraqi city, but missiles destroyed buildings and streets all over the area.

Speaking to The Washington Post's Erin Cunningham in January, a local lawmaker raised concerns about the future of the city following the offensive to liberate it.

"Ramadi is totally destroyed, there are no forces to secure the city, and there is no trust between the government and the people,” said Raed al-Dahlaki, a Sunni lawmaker.

Whereas Ramadi has a predominantly Sunni population, the Baghdad-based government is mainly composed of Shiite Muslims — a sectarian division that has contributed to the tensions in Iraq. "If the government is slow or unable to rebuild," Dahlaki said, "then there is no future for Sunnis in this country." The Iraqi government has focused on the continuing fight against ISIS, while reconstruction efforts have stalled amid declining oil revenues.

Former residents used to ask themselves how long it would take to rebuild the city. Now, they wonder whether it will ever fully be reconstructed at all.

As in Ramadi, Mosul's residents are mainly Sunnis. The future of cities with predominantly Sunni residents could become decisive for the future of Iraq as a united country.

Satellite photos show how entire apartment complexes were destroyed in the battle for Ramadi. Overall, more than 3 million people have been displaced by the fighting in Iraq.

Even after the liberation of cities such as Ramadi, former residents face major difficulties in trying to return. Before losing the city, ISIS militants booby-trapped some of the buildings that had not been destroyed by missiles. The U.N. High Commissioner for Refugees warned in April that residents returning to those buildings could risk death.

In Ramadi, liberation has come at a high cost.

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