There are two useful sources of information about what's happened in Syria and the Islamic world to fuel the current 'refugee crisis' in Europe and the upsurge in ISIL terrorist activities in the West.
First, Strategy Page brings us a useful analysis of 'What Failure Has In Common'.
The six worst violence hotspots on the planet at the moment (Iraq, Syria, Afghanistan, Yemen, Libya, Somalia) seem hopeless and the search for solutions seems futile. But when you step back and take a closer look you find that all these countries have lots in common, aside from being “failed states.” All are largely Moslem and all have serious problems with governing themselves. This spotlights the fact that Moslems in general and Arabs in particular have developed a peculiar relationship with democracy in an attempt to cure these longstanding problems.
There's more at the link. Useful information. I'm not so sure that democracy is, at present, the best possible solution for many of these states. I suggest that many of them need an Atatürk, a strong dictator to drag them kicking and screaming into modern times whether they want that or not, more than they do a one-person-one-vote scenario where the voters are neither educated nor informed. However, the problem with an Atatürk solution is that for every enlightened 'dictator', one gets a dozen self-interested despots who'll rule for their own benefit and that of their cronies, rather than the nation as a whole. How to get around that problem (apart from judicious assassination), I just don't know. (Turkey is experiencing precisely that right now with the Erdoğan administration, which is Islamic to the core and, despite the obligatory lip-service to his memory, probably regards Atatürk as an unfortunate historical aberration to be corrected as quickly as possible.)
Next, this video report from Vox examines how the current situation in Syria came to be. I generally don't trust Vox as an objective source, because the site's overtly left-wing, progressive perspective often colors its reporting, but in this case it seems reasonably balanced and accurate. Judge for yourself.
Putting those two sources together, the background to the Paris attacks and the current tensions in the Islamic world become much clearer.