Originally Posted by
The Lucky One
Yes. Contagion was a standalone crossover (I doubt Cataclysm or No Man's Land had even been dreamt up at the time) about a deadly plague hitting Gotham. It was followed some time later by Legacy, a follow-up about Ra's al Ghul and Bane allying and threatening to unleash a... different version of the same plague, I believe? (I haven't actually read it yet.) After that, another year or so went by and we got Cataclysm, about an earthquake hitting Gotham. That was followed by the stories now collected in "Road to No Man's Land" volume 1 (which mostly collects the "Aftershocks" stories) and the upcoming volume 2 (the actual "Road to No Man's Land" stories).
The stated in-story reason for the No Man's Land is that between the plague and the earthquake, Gotham wasn't worth salvaging, but we don't actually know when the writers and editors dreamed up the concept of NML... it might have been before, during, or after Cataclysm. Either way, if you want to focus purely on the crossovers, I believe it goes Knightfall/Knightquest/KnightsEnd/Prodigal (3 volumes), Contagion, Legacy (to be released later this year), Cataclysm, Road to No Man's Land (2 volumes), No Man's Land (4 volumes in the most recent printing). After that was, I think, Officer Down, then Bruce Wayne: Murderer/Fugitive, and (ugh) War Games, if you plan to keep going.