I don't know where you are at in your recovery but looking at upsetting past events ( at least in very early recovery) might only serve to make things more difficult.
Be careful of a trap that involves looking for a "reason" why you drink. Something you can pin down as the "cause" and perhaps as a justification.
If there was any one thing that "caused" me to be angry it was my own expectations. Sure, I have had plenty of nasty things happen to me, but the emotions they caused never justified my drinking. I had to find other, more healthy ways of dealing with these sorts of events, whether the were in the past or in the present.