The history of the Middle East is such a complex and tangled net, even relatively recent history is enough to make accomplished historians fumble. Reaching back even further into the mists of centuries past, there are, no doubt, factors which have fed into 20th and 21st century issues, but humble intellects such as my own simply cannot take it all in.
Putting a magnifying glass on just what's gone on in the 21st century until now, there has been much increased internal fighting between various religious factions within the Middle East. It does appear that the US invasion of Iraq has been instrumental in growing extra factions of militants who will try, in any way they can, to avenge destruction they have seen perpetrated by Western powers during their lifetimes, not only by USA governments and forces, but by the militaries and governments of France, UK, and other European countries. Governments of these Western nations have meddled in the Middle East for decades for their own gain. This has been in tandem with constant in-fighting among religious or political Middle Eastern factions.
All that this combined madness accomplishes is a never-ending cycle of death and destruction. Yesterday French fighter planes dropped 20 bombs on an ISIS stronghold and training camp in Syria. May that be an end to it!
I do hope cool heads will prevail in coming weeks.