The cause is pretty simple, the region is in major turmoil, the roots of which are many and complicated. There is truth to the fact that the US invasion of Iraq was partly to blame, the country we left after Hussein was unstable, and it allowed a power gap that a group like ISIS could exploit (not to mention that Sunni muslims, a minority in the country, felt powerless and ended up supporting ISIS, which is Sunni). Western governments are against Assad, the US in particular, because he poses a threat to Israel through Syrian support of Hamas and such, and when a rebellion started, the US supported the rebels, not surprisingly, which led to chaos, and again ISIS in the power vacuum took over. The migrants from Tunisia are fleeing what is basically a civil war after the “Arab Spring” everyone was enchanted by, others are coming from the mess in Egypt.
The other problem you have is that while ISIS is a major threat, you also have paralysis because regional rivalries stop the old “the enemy of my enemy is my friend”. ISIS is Sunni, as are the Saudis, and in part they will be reluctant to fight them, especially since ISIS is right now fighting the Iraq government, which is Shia, as is Iran.
The reason people are leaving is easy, it is desperation, it is all well and good to talk about fighting ISIS, fighting Assad, but when you are living places that have been destroyed, where feeding a family is impossible, where there is no hope, how the hell do you fight? With what? What you are seeing is the cracks that have been there a long time opening up, we all talked about the horrible dictators in the middle east, and they were/are, but no one thought of the consequences of removing them. Anyone remember the horrors of the old Yugoslavia falling apart, the genocide and continuous fighting? The only reason we didn’t see there on a large scale what we see with ISIS in the middle east is that in the cause of Bosnia and such, outside countries acted to rectify the situation.
Lot’s of guilty parties. However, one thing to think about is when the US refused to take Hussein out of power back in the first gulf war, Dick Cheney made the comment that if they had removed Hussein, who would take over in the power vacuum that would follow, and how much further misery and suffering would happen? The inconsistent and conflicting policy in the region by almost everyone led to this kind of mess, it isn’t the US’s fault, it isn’t the fault of ‘military weakness’, it is a festering mess that has been allowed to fester for many years. Put it this way, even if we spend 2 trillion a year on defense, what good would it do? Our military was at full strength when we went into Afghanistan and Iraq, and look at the end result there, what a mess it was after the initial victory. Yes, ISIS is going to need to be stopped militarily, but it is going to take a multi lateral response and is going to involve a lot of things. It is going to involve trying to solve the Syrian mess one way or the other, it is going to involve containing ISIS and more importantly, figuring out how to shut down their financing. It is going to take a UN that hasn’t decided it is the cheering section for anything third world, and put together some kind of plan of action, which so far it has shown basically no response to ISIS or the refugee crisis. It is also going to take real leadership across the board, which so far no one has shown.