A breakaway from terrorist organization al Qaeda, "Islamic State" is a Sunni militant group that is believed to have formed in response to disillusionment and frustration due to the failed rule of governments in Syria and Iraq. Its flag reads "Muhammad is the prophet of God" and "There is no god apart from Allah" - lines that are valid for all Muslims, not just "IS."

The "Islamic State" aims to create a "caliphate" - a state where the traditional values of Islam and Sharia law must be adhered to. Due to the instability of regions in Syria and Iraq, the "Islamic State" has been able to capture land in the two countries.

A key difference is the brutality "Islamic State" has used to strike fear into its enemies and innocents by cruel beheadings and ruthless violence. In contrast to this, it is said to govern the regions it takes over. As Middle East expert Shadi Hamid told PBS: "They provide social services. They run local government. They provide some modicum of law and order."

Though "IS" is active in Syria and Iraq, the Nigerian terrorist organization Boko Haram recently declared its support. It's like a competition in cruelty: while Boko Haram is responsible for 13,000 deaths, "IS" has injured or killed at least 24,000 people. Terrorist group al Qaeda has distanced itself from "IS" with its offshoot Nusra Front even fighting against "IS".

Something else that distinguishes the "IS" is its followers. More than 20,000 foreign fighters have joined the group, with more than 4,000 come from Western Europe and North America, according to an ICSR report. Here are the countries where most people have gone to fight. But, there are more fighters per capita heading to fight from some smaller countries like Sweden and Belgium.

Since August 2014, a US-led coalition has carried out airstrikes on "Islamic State" targets in Syria (1,422 strikes) and Iraq (2,242 strikes), according to a BBC report. Some governments have also been active within their own countries: Germany is set to prosecute at least 30 suspected militants returning from Syria, while Saudi Arabia, for example, arrested 93 suspected militants in April 2015.

'Islamic State' militants ransacked and destroyed statues in a museum in Mosul, in northern Iraq. The idols were believed to be remnants of the ancient Mesopotamian civilization. The jihadis, who have taken over large swathes of Iraq and Syria, said their interpretation of Islam calls for the statues and relics to be destroyed. Many Muslim scholars denounced the group.

This is a picture of the ruins of the 2,000-year-old city of Hatra, built by the Seleucid Empire which controlled a large part of the then-known ancient world. IS militants were reportedly bringing in bulldozers to raze the ancient city. "Their battle is a battle for identity, to empty the region, primarily Iraq, of its human inheritance," Iraq's Tourism Minister Adel Shirshab said.

The militant group's members also destroyed party of Nineveh, an ancient city in northern Iraq and considered by many Western archaeologists to be the cradle of civilization. "It was expected that [IS] would destroy it," Tourism Minister Shirshab told journalists. The United Nation has called the destruction a "war crime."

"The sky is not in the hands of Iraqis...Therefore the international community must move with the means it has," Iraq's tourism minister said as he pleaded for air strikes against IS extremists. Baghdad has said that IS fighters were defying "the will of the world and the feelings of humanity."

IS militants claim the ancient statues run counter to their radical interpretation of Islam's tenets that prohibit idol worship. But when fighters aren't destroying the artifacts, they're cashing in on them. Experts have said the group is making money in the international market by selling smaller statues from ancient sites while destroying the bulky ones are destroyed.

Scholars often compare the IS' destruction of cultural heritage sites to how the Afghan Taliban destroyed ancient Buddhas of Bamiyan statues in 2001. Only a hollow remains where tall statues of the Buddha once stood. But some fear the damage caused by IS militants to the remains of the ancient Mesopotamian civilization, which pioneered agriculture and writing, could be more devastating.