Ruthless, well-funded, with tens of thousands of supporters and fighters, the "Islamic State" is constantly in the headlines as concern about Islamic violence rises.

Young Muslims, including converts, from all over Europe are headed to Syria and Iraq to fight for the militant group, originally known in the West as the "Islamic State in Iraq and Syria" (ISIS) - a new enemy spreading terror and barbarism, and clearly intent on expanding its territory.

In its latest move, the "Islamic State" terrorist network claimed responsibility for the deadly coordinated shootings and bombings in Paris on November 13.

Who are these jihadists?

The war in Syria had been raging for more than two years when in 2014, human rights organizations began to report on large-scale murders and massacres committed by IS militias in Syria.

In fact, IS extremists have been involved in the Syrian war since 2013 and active in the region for over ten years.

Out of Iraq

The network developed from an offshoot of the Al Qaeda terrorist group in Iraq.

When the US invaded Iraq in 2003, it toppled Saddam Hussein and ousted all his Sunni supporters from public service; many were arrested and imprisoned. Hundreds of thousands of Sunni Iraqis, including generals, officers, soldiers and civil servants, were pushed aside. Experts say that without that development in the wake of the US invasion, there would be no IS.

Led by Abu Musab al-Sarkawi, a group known as "Al Qaeda in Iraq" (AQI) formed in resistance to the US troops. The country was a magnet for jihadists, who, following al-Sarkawi's death in 2006, changed their name to the "Islamic State in Iraq" (ISI).

In early 2013, ISI took advantage of the power vacuum in Syria to expand their activities and numbers. They renamed themselves the "Islamic State in Iraq and Syria" (ISIS).

The group split from the Al-Nusra Front, previously the most successful Al Qaida militia in Syria. Al-Nusra had refused to give their allegiance to the group's military leader Ibrahim al-Badri - who has called himself Abu Bakr al-Baghdadi since 2010 and who had by then assumed command. Abu Bakr al-Baghdadi's aim is to establish a caliphate planned in Syria, Iraq, Lebanon and Palestine.

By the end of 2013, the terrorists had succeeded in establishing themselves in the northeastern Syrian province of Raqqa, using it as a base to conquer new territory.

Rise to power

Mosul, Iraq's second-largest city and the main retreat for former Saddam Hussein supporters, was next. When IS took control of the city in 2014, the group was soon joined by highly qualified Sunni former generals and fighters seeking revenge for the discriminatory policies of then-Prime Minister Nouri al-Maliki.

"The case of Mosul in June 2014 marked the real start of the expansion of the terror militia," Günter Meyer from the Center for Research on the Arab World at the University of Mainz said.

The IS looted the Iraqi central bank, which is based in Mosul, and pocketed millions of dollars.

Conquering territory

The jihadists advanced on the capital Bagdad while the Iraqi army fled in fear, leaving behind its most modern equipment and weapons without a fight. Al-Baghdadi, who rarely appears in public, announced the establishment of a caliphate in the areas occupied by the group, renamed his militia IS, declared international borders meaningless for himself and his followers - and enforced Sharia law.

A US-led coalition has been carrying out airstrikes on Islamic State positions in Iraq and Syria in response to ongoing IS offensives. Iraqi security forces in turn are conducting operations backed by American airstrikes, and Kurdish fighters in Syria have been recapturing towns and villages in northeastern Syria seized earlier by IS.

Shocking propaganda videos

The terror network is well-funded thanks to revenues from numerous gas and oil fields that generate millions of dollars every month, taxes and tariffs it imposes on conquered territory and protection and ransom money it extorts.

And it shocks the world with videos showing the execution of western journalists, aid workers and opposition fighters.

It's propaganda that isn't only aimed at new recruits, according to Peter Busch, senior lecturer at the Department of War Studies at King's College in London. "It's aimed at people who already belong to the group, and can also be seen as a demonstration of power," he said, adding that the videos are also aimed at IS' opponents.

"IS wants to discredit internal opponents, such as al Qaeda. But the material is also meant to shock Western governments and force them to act."

But the "Islamic State" is much more than a terrorist organization, cautions Christoph Günther, Islam expert at the University of Leipzig: "It's a movement trying to build a state, somewhere in between a social movement and a para-state." In some areas, the IS manages public services and provides water, electricity and schooling. That explains the attraction to a certain degree, Günther told DW, adding that he can very well imagine that the West might have to negotiate with the group one day.