This year, a coalition of forces inflicted heavy damage on ISIL, which lost almost all of its self-proclaimed "caliphate" in Iraq and Syria, but analysts warn the group is adapting and remains a threat to world peace and security.
Within hours of the start of the year, an Uzbek who described himself as a "caliphate soldier" sprayed a nightclub in Istanbul in Turkey with bullets from an automatic rifle, murdering 39 New Year's Eve revellers.
By directly arming extremists or by luring them with online propaganda, ISIL has committed or inspired dozens of deadly attacks, especially during the first half of the year, including in Pakistan, Iraq, Syria, Afghanistan, Egypt, Somalia and Great Britain.
Among them was suicide bomber Salman Abedi, a young British man of Libyan origin who killed 22 people — including many children — by blowing up a homemade bomb at the exit of an Ariana Grande pop concert in Manchester on May 22.
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Editorial: Iraq has defeated ISIL but there are formidable challenges ahead
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Vehicle attacks, committed by jihadists inspired by ISIL orders, have brought bloodshed to the streets of Jerusalem, London, Stockholm, New York and Barcelona — and are very difficult to prevent.
The attacks, which claimed several thousand lives overall, took place despite the near collapse of the organisation in Iraq and Syria, following an offensive launched in autumn last year.
ISIL had set up a base to manage its networks abroad, recruit soldiers, finance and co-ordinate their actions. But defeat as a conventional fighting force did not put an end to the attacks. "ISIL certainly is defeated militarily," said Yves Trotignon, a consultant, risk analyst and a professor at the Sciences Po, a private university in Paris.
"While it has about 3,000 fighters in Syria and Iraq, which is a lot, it should be remembered that in 2009 the predecessor of the Islamic State of Iraq had been militarily defeated. But it took them only two and a half years to take advantage of the Syrian revolution and rise again from the ashes."
The way in which the post-ISIL world is managed in the coming years will prove crucial in preventing extremists within the Sunni community from creating another militant movement claiming to defend its interests, according to experts.
In the meantime, the long list of attacks or failed attempts of this year proves that the global extremist movement — including Al Qaeda — remains resilient.
"The surgical operation in Iraq and Syria has been successful. But, as was the case in Afghanistan with Al Qaeda, the cancer has regrown and there are jihadist territories elsewhere," Mr Trotignon said.
"ISIL is defeated, but the terrorist threat is far from disappearing. It is evolving in terms of the protagonists, modes of operation, and no calming factor is emerging.
"American researchers believe the phenomenon will last several generations."
US Col Ryan Dillon, spokesman for the US-led anti-ISIL coalition, said recently: "They are no longer a military threat. They no longer have an army like in 2014. It does not mark the end of Daesh."
The withdrawal of American forces has begun. On November 30, the Pentagon announced that 400 Marines in Syria would return to the United States.
Although it was not explicitly claimed by ISIL, the massacre in late November of 305 Sufi worshippers — considered as heretics by the extremists — at Al Rawda mosque in northern Egypt may hint at a move towards more lethal and indiscriminate guerilla actions by extremists.
"The subsidiaries of Daesh, primarily in Egypt, but also in Libya, Yemen, Afghanistan and South-East Asia, remain very threatening," according to Jean-Pierre Filiu, professor at Sciences Po.
"And jihadist propaganda, although less intense than in the days of the pseudo-caliphate, continues to maintain its mission and networks throughout the world."