As Deez has pointed out, while many news agencies have reported this was ISIS, even ISIS claimed responsibility, we don't know of ISIS Actual funded, planned, and executed the attack.
That said, this was an attack, one of many, in the past several years, by Islamic extremists. But that's not the whole story. This was an attack, one of many, over the past decade, over the past century, since the beginning or the American Republic (before oil, or an overseas military presence, or the State of Israel), and since the beginning of Islam 1,500 years ago. The cause of these attacks aren't Obama, or W. Bush, or Clinton, or GHWB, or Regan, or Carter. They aren't because of the West Bank or Gaza Strip. They aren't because of Gorbachev, or Lawrence of Arabia, or colonialism.
Jihad, struggle, is simply the way it's been for the vast majority of human civilization. It's not caused by anything anyone does. It is the way of life. Electing a kinder POTUS (at least optically) did nothing to solve the problem of Islamic extremism because they don't care if the President was General LeMay or Mother Teresa.
You're certain nobody has an answer to ISIS. I don't know if that's true or untrue. I have a few ideas - maybe they'd work...maybe they wouldn't. But here's what I know for certain. For Americans and our allies, this fight is not about these f#@^!* Islamic extremists. They are nothing and will always be jihadists. This is about who we are. What is France? What is America? There are a lot of answers, all correct to those two questions and too many to count culturally, technologically, religiously, politically, philanthropically, scientifically. etc. And we don't need "jobs" to define how great America and France are or as a reason to be great.
As the Marquis De LaFayette wrote, "Humanity has gained its suit (America); Liberty will nevermore be without an asylum." Notice how he said "Humanity." To make good on this, the Marquis believed Americans would fight for liberty. The price of Liberty is eternal vigilance. It's not taking out Jihadi John collecting $200 and passing go. It's not some quantitative metric on neutralized high-value targets, reduction in terrorist attacks, or successful Justice Department prosecutions. Eternal vigilance, the price of Liberty and standing up for who we are, is kicking *** 24/7/365 eternally whenever anyone threatens Columbia. It is standing up for Liberty anywhere in the world when decency is threatened. And LaFayette was not some pansy that half-assed $%i+. It is the belief in and protecting the suit of Humanity. That is what winning this war means to France and America.