Incidentally, you have said that you thought we would attack you, and therefore made preparations; and we have likewise been convinced that you would attack us, and as the weaker party we went for the pre-emptive strike.
Precedent. You attack your neighbors one after one, expanding by war and annexation. Foels claims my realm all the way to Egypt, why would he do that if not in preparation to take said land from me? Likewise he claims land halfway up Russia, and did you not try to wrest a third of Russia from vR not long ago? Claims+history of conflict = reasonable suspicion. As for us attacking, how often do I attack? I never do, do I? War is not my thing, I expand diplomatically, by vassal-sniping. The Fatimids may rattle sabers, but they don't seem in terrible haste to actually put their asses on the line.
Second: Russia. You attacked him despite the fact that he had never attacked you, and with demands not exactly small. Is it strange then that we expect you to do again what you have done repeatedly before?
I was perfectly happy with just the Fatimid vanilla startpos in the levant. When I reached it I offered Foels long-term peace and recognition of our border, he in not to veiled terms informed me he intended to take it away from me. So expecting he would do exactly what he told me he intended to do I started sniping his vassals so he would have less regiments with which to attack me, and thus I gained most of Iraq as buffer for the coming assault.
In the same vein I do not seek Baghdad because I want it as such, but because after Persia has attacked me for the third time and repeatedly voiced intent to take even larger swats of my land (again he wouldn't have claimed all that land unless he intended to take it), I seek a solution to make him unable to do so. That solution is to sufficiently weaken his ability to hurt me, as apparently even defensively allying Russia is not sufficient to not get attacked.
Now obviously we come to the problem that our best (and often only effective) defense is offensive conquest. As thus we attack players who we perceive as threats, but with the main intention of defending ourselves from feared aggression. The side who is getting occupied will of course not be terribly likely to agree with that definition of "defense". In this our little game is quite similar to history, after all how many nations have not claimed their every war was in self defense?