The group known as Islamic State of Iraq and Syria executed a second American journalist, Steven Sotloff, last week in response to President Obama’s foreign policy and U.S. airstrikes in the region where ISIS operates, according to a ISIS fighter and Sotloff in what appeared to be a forced statement in the video of his execution.

ISIS, officially known as the Islamic State of Iraq and the Levant, is a Sunni terrorist organization operating in Iraq and the Levant region, according to the National Counterterrorism Center, a U.S. government organization that provides information on terrorist groups.

According to the Council on Foreign Relations, the goal of ISIS is to establish a caliphate: an Islamic state that is ruled under sharia law.

ISIS is lead by a man referred to as Abu Bakr al-Baghdadi, but his followers know him as Caliph Ibrahim, reports the BBC. Baghdadi claims to be the Caliph: leader of all Muslims, and a descendent of the Prophet Muhammad.

The group was formed by Abu Musab al-Zarqawi in April 2004 as al-Qaida in Iraq, according to the NCTC. The group pledged allegiance to Osama bin Laden in 2004 and has been involved in attacks against coalition forces and civilians in Iraq, often using tactics such as vehicle born improvised explosive devices, suicide bombers, and executions by beheading.

“Osama bin Laden and Zawahiri believed al-Qaida in Iraq’s indiscriminate attacks on fellow Muslims would erode public support for al-Qaida in the region,” CFR reported. “In July 2005 they questioned Zarqawi’s strategy in written correspondence.”

In 2006, a U.S. airstrike killed Zarqawi, and Abu Ayyuab al-Marsi took command as al-Qaida in Iraq’s new leader, reports CFR. A few months after taking command, Marsi changed the group’s name to Islamic State of Iraq to improve local support, which was dwindling from the group’s attacks on Shiite sites and the killing of Muslims, just as bin Laden and Zawahiri anticipated.

According to the NCTC, Baghdadi became the group’s leader after Marsi was killed in 2010. During the first half of 2013 the group caused about 1,000 Iraqi deaths, the most deaths seen since 2008. In April of 2013 the group stated that it was operating in Syria and changed its name to the Islamic State of Iraq and the Levant.

ISIS is just one of many jihadist and rebel groups fighting the regime in Syria, according the BBC. ISIS has a strained relationship with al-Nusra, the official al-Qaida affiliate in Syria, and many other rebel groups. Zawahiri, the leader of al-Qaida ordered ISIS to leave Syria and focus on Iraq, but Baghdadi refused.

“In January 2014, rebels from both Western-backed and Islamist groups launched an offensive against ISIS, seeking to drive its predominantly foreign fighters out of Syria,” reported the BBC.

Thousands have been reported killed in the fighting.

ISIS has made headlines for their adept usage of social media as a recruitment tool. The group has put out recruitment videos and internet memes to target westerners. These efforts have paid off.

According to the Soufan Group, a private intelligence organization, as of June there were over 12,000 foreign fighters from at least 81 different countries fighting in Syria. Of those, approximately 2,500 of them are from Western countries including most members of the European Union, the United States, Canada, Australia, and New Zealand.

Dr. Howard Stoffer, an associate professor for the national security program at the University of New Haven, said that these fighters represent a huge threat when they return to their home countries with the ability to build explosives and use weapons with the ideology that they are going to fight the governments of Western Europe and North America.

Stoffer, who also served on the United Nation’s counter-terrorism committee, said that he think’s ISIS has suddenly gained so much attention because of the speed in which they crossed western Iraq, almost making it within striking distance of Baghdad. He said that the group is also notable for their absolute brutality in the areas they govern, specifically beheadings of people they subjugate and starving of minorities that ran to the Sinjar Mountains.

“They are an urgent problem, a force that is living in medieval times in terms of the types of religious and administrative law they want to implement,” Stoffer said. “They threaten the vitality of Syria and Iraq as states, and if they succeed there, they can then threaten Turkey, Jordan, Lebanon, and Israel.”

The strength of ISIS forces is difficult to know, but it is estimated to be between 10,000 to 15,000 fighters, said Stoffer. At this point in time, ISIS is probably not capable of a strike on the U.S. or Canada and may not even be able to strike Western Europe, but Stoffer believes that they are capable of threating important allies of the U.S. in the region where they operate.

“For those reasons, I would say that their capability in the region is perhaps greater than al-Qaida’s was, but just in that region, not in the Maghreb of Northern Africa, and not in the Arabian Peninsula where al-Qaida is functioning, or in Somalia where al-Shabab is functioning, or in Asia,” Stoffer said. “Within the Middle East region, I think they are a greater threat than al-Qaida was, but on a global basis I don’t think they have achieved the capability al-Qaida had around the time of September 11.”