To be fair, I've heard of many of these Arab sects holding grudges that go on for millennium... 50 years is probably nothing to them. ;)

Much of today's issues in the region are firmly rooted in the same issues that lead to WWI and never got resolved.

Here's the problem: we're fighting a guerrilla war with people who are still upset about the crusades.

And the other side (so far as the combatants are concerned) still wanted their homeland back after 2000 years or so.

But the point remains solid I think. While you can probably always find someone earlier with which to share the blame, the primarily relevant thing is who it is currently within our power to hold responsible. Not that anybody should be wrongly held responsible, just that having shared responsibility doesn't absolve you of any.

And recognizing that you played a role in creating the situation that allowed a horrible act is also not the same as saying you are to blame for it happening and that others are absolved.