The Islamic State of Iraq and Syria, also called the Islamic State of Iraq and the Levant, has garnered countless headlines across the globe.
Their atrocities against religious minorities and effort to create an Islamic state in the Middle East have spurred international outrage as well as U.S. airstrikes.
Below are four important points about ISIS, specifically its origins, military engagement, atrocities and denunciations from Muslim leaders.
ISIS' beginnings can be traced to the Second Gulf War in 2003, when the U.S., along with a small coalition of other nations, invaded Iraq and toppled dictator Saddam Hussein.
Amongst the diverse insurgency fighting coalition forces and new Iraqi government was the extremist Islamic group al-Qaida in Iraq.
ISIS was formed out of the al-Qaida affiliate in April of last year and led by Abu Bakr al-Baghdadi, a mysterious jihadist who is believed to have been born in Iraq in 1971.
Initially centered on Iraq and known as the Islamic State of Iraq (ISI), ISIS added the second S for Syria to its name as that nation's civil war erupted several years ago, according to Aaron Y. Zelin of the Washington Institute.
"In late summer 2011, ISI leader Abu Bakr al-Baghdadi dispatched operatives to Syria to set up a new jihadist organization," wrote Zelin back in 2013.
"Among them was Abu Muhammad al-Jawlani, the leader of what would become JN, which officially announced itself in late January 2012. … Due to these successes, Baghdadi changed the name of his group from ISI to ISIS in April 2013."
Wins and losses
Drawing their origins from earlier incarnations of jihadist organizations in the Middle East, ISIS has come to hold territory in both Syria and Iraq.
As Syria continues to be divided by civil war, ISIS has seized parts of the eastern portion of the country. ISIS gained much attention when it took the major Iraqi city of Mosul back in June.
Part of the conquest included taking control of the Mosul Dam, the largest dam in the country, raising the threat that ISIS militants might intentionally flood much of the region.
The British Broadcasting Corporation noted that ISIS has had major military victories both before and after adopting its present appellation.
"The group has seen considerable military success. In March 2013, it took over the Syrian city of Raqqa — the first provincial capital to fall under rebel control," noted BBC.
"In January 2014, it capitalized on growing tension between Iraq's Sunni minority and Shia-led government by taking control of the predominantly Sunni city of Fallujah, in the western province of Anbar."
In response to their successes and attacks on various groups, the U.S. recently began launching airstrikes against the organization and Kurds in Northern Iraq have been fighting back.
Daniel Byman, professor at Georgetown University and research director of the Saban Center for Middle East Policy at the Brookings Institution, recently wrote that ISIS' aura of invincibility speaks less to their talent as it does the lacking effectiveness of their opponents.
"The United States has provided billions of dollars worth of military equipment to the Iraqi army, which on paper far outnumbers and outguns IS. The catch is that the Iraqi army will not fight," wrote Byman for The Washington Post.
"[Prime Minister Nouri al-Maliki] appointed political loyalists, not competent leaders, as its senior officers. The regime's discrimination against Iraq's Sunnis has undermined morale among Sunni soldiers, who don't want to fight for a government they despise."
ISIS has garnered international outrage for its brutal treatment of religious minorities and fellow Muslims in the territory they occupy in Syria and Iraq.
Allegations of varying validity have included reports of beheadings, massacres of prisoners, and attempts to exterminate Christian communities.
This penchant for violence against diverse groups under their rule has existed in ISIS' earlier incarnation as al-Qaida in Iraq and led to a backlash from Iraqi militia groups in 2007.
On Aug. 14, United Nations special representatives released a joint statement calling for the highest level of humanitarian in Iraq because of ISIS.
"We are gravely concerned by continued reports of acts of violence, including sexual violence against women and teenage girls and boys belonging to Iraqi minorities," read the statement in part.
"Atrocious accounts of abduction and detention of Yazidi, Christian, as well as Turkomen and Shabak women, girls and boys, and reports of savage rapes, are reaching us in an alarming manner."
The UN estimated that as many as 1,500 Yazidi and Christian persons were forced into sexual slavery and tens of thousands have been forced from their homes.
Islamic opposition to ISIS
The ideology and atrocities of ISIS have led to them finding opposition from various Islamic leaders and groups.
In August, the Indonesian government banned support for ISIS after the Middle Eastern terrorist group attempted to recruit members from the world's most populous Muslim nation.
Not long after Indonesia's action, influential Egyptian cleric Grand Mufti Shawqi Allam, declared on state news agency MENA that ISIS "poses a danger to Islam and Muslims."
"An extremist and bloody group such as this poses a danger to Islam and Muslims, tarnishing its image as well as shedding blood and spreading corruption," said Allam.
"[They] give an opportunity for those who seek to harm us, to destroy us and interfere in our affairs with the [pretext of a] call to fight terrorism."
Byman of Brookings wrote that ISIS is on bad terms with al-Qaida, as the two entities were once allies but presently are "bitter enemies."
"Al-Qaeda and IS differ on tactics, strategy and leadership. IS leader Abu Bakr al-Baghdadi embraces beheadings and crucifixions, and he focuses on local regimes and rivals, ignoring [al Qaida leader Ayman al-Zawahiri's] credo of hitting the 'far enemy' — the United States," wrote Byman.
"These differences came to a head in Syria, when Zawahiri designated the relatively more restrained Jabhat al-Nusra (JN) as al-Qaeda's local affiliate. Baghdadi believes that his group should be in charge of jihadist operations in Iraq, Syria, Lebanon and Jordan. The two groups turned on each other, with their infighting reportedly killing thousands."
Despite the many enemies, ISIS remains a powerful force in the region. They control several oil wells and reportedly receive much private funding from parties in various Arab countries.