Determined, as President Barack Obama said, to “degrade and destroy” militants of the Islamic State group, the U.S. and its Arab allies bombed Raqqa, Syria, early Tuesday. In three months, ISIS has taken over large swaths of land in Syria and Iraq, using Raqqa as a de-facto headquarters to facilitate the fighting with weapons and soldiers. If the U.S. and Arab bombing campaign can hobble ISIS in Raqqa, the Sunni militant group’s momentum would be halted -- at least for now.

The bombings in the Raqqa region marked the first outside military intervention in Syria in the three-year-old civil war that has killed more than 190,000 people and displaced more than five million, according to United Nations estimates.

While the rebels in Syria have called on the U.S. to intervene in the war to topple the Bashar Assad regime, Obama hesitated to engage militarily. After a decade of war in Afghanistan and Iraq, the American public has had no appetite for more combat abroad. But the viciousness of ISIS actions -- beheading U.S. journalists James Foley and Steven Sotloff, and British aid worker David Haines, threatening to kill more of its hostages, and forcing tens of thousands to flee -- forced Obama’s hand.

In a speech earlier this month Obama vowed to “hunt down terrorists who threaten our country, wherever they are,” adding: "If you threaten America, you will find no safe haven." In the speech, Obama, for the first time, described ISIS as a security threat to the United States.

According to the Syrian Observatory for Human Rights, a monitoring group in Syria, “tens” of ISIS fighters were killed in the Tuesday bombing strikes. The Pentagon reported that U.S. Central Command, or CENTCOM, had hit 20 targets, including militant fighters as well as training sites, command-and-control sites, troop encampments and weapons depots.

“I can confirm that U.S. military and partner nation forces are undertaking military action against ISIL terrorists in Syria,” said Pentagon press secretary Rear Adm. John Kirby in a statement.

Several other countries also participated in the airstrikes, including Jordan, Saudi Arabia, Bahrain and the United Arab Emirates, which recently launched an air campaign on militants in Libya. The U.S. had not officially released the list of its partners in the international coalition to combat ISIS, but the presence of Arab partners testifies to the nervousness that the Islamic State group’s ambitions -- and its military success -- have stirred up in the region.

The airstrikes by the U.S. in Syria are in addition to the ones that have been launched on ISIS targets in Iraq: more than 190, according to the State Department. If the U.S. and its allies successfully destroy ISIS weapon stocks in Raqqa, it could significantly curtail the group’s military capability in Iraq and Syria.

Raqqa is strategic for ISIS both geographically and tactically. The city is located in the northern part of Syria. Because the group controls the roads around Raqqa, it can easily access key eastern cities like Deir Ezzor and towns on the Iraqi border.

ISIS seized the 17th division Syrian army base in Raqqa at the end of July. Jabhat al-Nusra, the al Qaeda’s affiliate in Syria, had originally taken control of the city from President Bashar Assad’s forces in March 2013, at a time when ISIS and Al-Nusra coordinated fighting against the regime. The two groups, though still battling government forces, are now vying for power and resources.

The Islamic State group used Raqqa as a weapon distribution center. When it took control of Mosul, Iraq’s second largest city, on June 10, it bulldozed the border between the two countries, allowing for the free flow of fighters, weapons and other lucrative resources. It transported the majority of the weapons it seized during its offensive in Iraqi Kurdistan to Raqqa.

Taking control of Raqqa has also allowed the group to move its offensive west to Aleppo, the economic capital of the country, known predominantly for its textile industry. Over the past month, ISIS has attempted to take control of suburbs in northern Aleppo province near the Turkish border. The group now controls a piece of land that stretches from northern Aleppo all the way to Baghdad.

According to activists in the city, under ISIS rule people have witnessed crucifixions, murders and alleged beheadings. Residents told Syria Deeply, a news agency monitoring the Syrian civil war, that ever since the Sunni militant group began making gains in the city, buildings have been painted black and women have been forced to cover their faces. The militant group has also killed minority groups in the area, predominantly Shiites.

The airstrikes marked a new phase of U.S. policy in Syria. Until now, the Obama administration has resorted to fighting the Assad regime by arming and training the moderate opposition. The U.S. has tried to support the opposition in an attempt to level the playing field between those fighters under the Free Syrian Army and the Syrian military. It never initiated, at least publicly, a plan to take out ISIS or other extremist organizations.

It is unclear what repercussions the air campaign might have for the U.S. and others involved. ISIS is currently holding other hostages and military action could threaten their lives, and the White House said Monday that some ISIS fighters had returned from Syria to the U.S, possibly increasing the chances of an attack on American soil.

Obama and Secretary of State John Kerry have insisted they will not put U.S. combat troops on the ground, so the success of the mission -- which is still only hazily defined -- depends on the air campaign that started Tuesday morning. When morning breaks in Syria, the damage inflicted on Raqqa may become clear. And that will be the first sign of how well this new battle is going and how much more it may take to win.

Correction: A previous version of this story incorrectly stated that British hostage Alan Henning had appeared in an ISIS video showing the beheading of captives. He has not. The story has been amended.