Jim Michaels

USA TODAY

U.S.-backed Iraqi forces seized the center of Fallujah Friday, a significant breakthrough in the battle against the Islamic State, which has controlled the city for two years.

The battle is far from over but holding the city center gives government troops a tactical edge and a morale boost.

Here are the five reasons why driving the militant group from Fallujah is so important to the Iraqi government and U.S.-led coalition supporting its offensive to retake the city.

1. GROWING HUMANITARIAN CRISIS. Aid groups and civilians trapped in Fallujah say starvation and other deprivations inside the city are worsening. Civilians trying to flee the city have been shot by militants, according to eyewitness reports. The dire developments have prompted Sunni leaders to press Iraq's Shiite-dominated government to take action in the face of the growing humanitarian crisis.

2. STRATEGIC LOCATION. Fallujah is less than 40 miles from Baghdad and straddles key roads into the Iraqi capital. In recent weeks, the Islamic State has detonated large vehicle bombs inside the city. Securing Fallujah would help cut off a militant supply line into Baghdad and deter bombings there.

3. IMPORTANT SYMBOL. Fallujah is an influential Sunni city and among the first Iraqi cities to fall to the Islamic State two years ago. Some tribes within the city have supported the Islamic State, made up of fellow Sunnis. Other tribes have taken up arms against the radical jihadists, who have exploited sectarian conflicts between Iraqi Sunnis and the Shiites who dominate the country and its government. In 2004, four U.S. contractors were killed by a mob in Fallujah and the charred remains of two of the men were hung from a bridge over the Euphrates River. A U.S.-led offensive secured the city months later, but it had become a festering symbol of resistance to the U.S. occupation. A key risk now: Shiite militias participating in the offensive could abuse Sunnis, allowing sectarian tensions to flare anew.

4. PRELUDE TO MOSUL CAMPAIGN. Securing Fallujah will help set up a more significant offensive to drive the militants out of Mosul, Iraq's second largest city. Liberating Fallujah will be a major step in clearing the surrounding Anbar province, a large Sunni region south of Mosul. That would help isolate Mosul, making it difficult for militants to get reinforcements when Iraqi forces attack the city. The Fallujah operation may delay the Mosul offensive, however, because it has siphoned off forces that would have to be replenished to retake the northern Iraq city.

5. CONFIDENCE BOOST. It is the last major city other than Mosul held by the Islamic State, and a victory there would bolster the confidence of the U.S.-backed Iraqi forces. In December, they cleared Ramadi, the capital of Anbar province, hailed as a major victory for Iraq's government. Countrywide, the Islamic State has lost about 45% of the territory it once held in Iraq. Recapturing Fallujah would build momentum toward the Mosul offensive and lend that offensive a sense of inevitability.