What is much more interesting/worrying than any lone wolf / homegrown or not discussion is why ISIS, be it by leading locals spiritually or by actually training/sending people, have turned their strategy 180?. Until now, ISIS focused on building themselves into a local power to be reckoned with by being ruthless in their local expansion strategy and staying out of global politics. Yep, there's has been some alibi anti-ISIS bombing and drone warfare, but it's the main reason the west has left them more or less alone so far.
By attacking targets in the West (and maybe downing a Russian airliner as well) they are provoking a major international strike against them that is almost guaranteed to take a bunch of the territory they gained away from them. It seems like the most stupid move in the history of expansive warfare.
And while I won't even comment on most of the racist shit Delll spouts, he's right in one point: A war against ISIS can only be won by ground troops. In fact, sending in a decent amount of soldiers instead of arming ISIS to fight Assad would probably have prevented this shit from happening. But as long as the West fears the images of soldiers returning home in body bags by the dozen, the terrorist threat will not be stopped: You can destroy a country with air strikes, but you can't control it without a guy with a gun on every street corner. And you need to do the latter to stop terrorism. Thus, another bombing campaign will only make stuff worse. Send in ground troops, disarm these assheads and stay until civil society is fully restored. Even if it takes a dozen years or more. The Americans stayed in Germany for more than 40 years after WW II to make sure civil society would work. The West has to do the same next time they try to fight terror in the middle east.