If there is a logic and a rationale for the horrific acts of terror that were committed in Paris on Friday, they are accessible to a very few people. All sane and humane persons should recoil with horror at those atrocities. There can be no excuse or justification for the murder of at least 129 people. The perpetrators are dead but there were others involved in the planning and execution; they must be found and punished. And the political movement and organization that motivates, applauds and facilitates these acts must be eradicated.

At least seven people executed multiple, virtually simultaneous bombings and assaults across Paris Friday night. A group of armed men entered the Bataclan concert hall, where the crowd was waiting for the headline act, and shot randomly into the audience. It is estimated that nearly 100 people were murdered before anti-terrorist commandos launched a counter attack, killing the gunmen and rescuing dozens of others.

At virtually the same time, gunmen attacked diners eating outdoors at several restaurants in central Paris and two suicide bombers blew themselves up outside the national stadium where the French and German soccer teams were holding a “friendly” international match. The two explosions were initially thought to be fireworks, and the game continued without interruption. Several of the attacks occurred near the former officers of Charlie Hebdo, the satirical weekly news magazine that was attacked by Islamic gunmen in January and left 18 people dead.

Hours later, French President Francois Hollande addressed the nation, calling the attacks “a horror” and pledged that the government would wage a “merciless” fight against terrorism. Parisians were told to stay home and offer shelter to anyone caught on the streets.

Witnesses said they heard the gunmen shouting Islamic slogans and condemning France’s role in fighting militants in Syria as they fired into the crowd. Hollande said, “We know where these attacks are coming from, who these criminals are, who these terrorists are,” although he did not identify any specific group. Later he called the attacks “an act of war … committed by a terrorist army, the Islamic State, against France, against … what we are, a free country.”

Shortly later, the Islamic State militant group claimed responsibility for the savagery, saying in a statement, released in French and Arabic, that “soldiers of Caliphate targeted the capital of abomination and perversion.”

International condemnation was quick. U.S. President Barack Obama called them “attack against all of humanity,” while United Nations Secretary-General Ban Ki-moon condemned “the despicable terrorist attacks.” Speaking for Japanese, Foreign Minister Fumio Kishida said “we strongly condemn the act of terrorism, which we do not tolerate for any reason.”

A united front is the only solution. France was struck by terrorists in January — in the Charlie Hebdo attack. But Islamic State militants attacked a Shiite district in Beirut, Lebanon, days ago, and the group has taken credit for the recent downing of a Russian tourist aircraft that crashed in the Sinai Peninsula. In August, a lone militant tried to assault a high-speed train in Europe, but that attack was thwarted by passengers.

France is an important target for radical Muslims as it has been prominent in the fight against the Islamic State, joining the U.S.-led coalition battling the group in Iraq and Syria, as well as leading efforts in Africa to confront and defeat Islamic groups on that continent. As the host of a global conference on climate change to be held in Paris in a few weeks, experts have worried about the possibility of an attack.

France’s large Muslim community is increasingly restive and unhappy with its fortunes. The relationship between that community and the mainstream of French society is increasingly strained, the product of dwindling economic opportunities, a failure of assimilation and anger at economic, social and foreign polices. It is reckoned that as many as 1,500 French citizens have traveled to the Middle East to join the militants in their efforts to establish a caliphate. It is thought that several hundred have already returned to France, many of them eager to continue to wage the war at home.

Authorities have long worried about the prospect of “lone wolf” attacks, in which discrete individuals commit terrorist acts without being dispatched or coordinated by some larger organization. Experts have long feared that the large population of militarily trained and socially alienated Muslims in France makes that an increasingly strong possibility. The recent string of terrorist incidents in France suggests that threat has become a reality.

Some will claim that terrorism in France is the outgrowth of a foreign policy that is expansive and oppressive, that Paris has made itself a target for such actions. Nothing could be further from the truth. The battle against the Islamic State militants and like-minded groups is a battle against extremism: a fight against those who behead civilians, would deny all rights — and in some cases are prepared to exterminate — those with different religious beliefs and who believe that there can be no coexistence with nonbelievers. This is indeed a war and we must be prepared for more such acts of horror.

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