I hoped we were going to see some more flashbacks after the one at the beginning of season 2 - where they were stuck in traffic.
And it's back in just over 3 weeks!
Robert Kirkman has always said he's not interested in telling that story of how it happened and why. It's a story of survival against all odds and how people change and adapt to that situation and who they become. So I wouldn't hold your breath on many more flashbacks to the beginning, then again, a new show runner could change that but I think it would detract from how far the show and characters have come.
The best flashback which kind of explained the beginning, was with Lori and Shane looking over Atlanta being Napalmed whilst they stood there watching in horror. That just shows me how bad it must have been.