Since Romeo made Night Of the Living zombie films have become HUGE. Yet, it wasn't until slasher films came into the picture along with political and social unrest of the 70s that there was more zombie films.
I say this because when you look back in the 30s to 1969 zombie films were based on voodoo and witchcraft. Not the living dead looking for flesh that we now are associated with. Many people go for these types of films I feel because we want an escape from our humdrum lives. So what better way than to watch a bunch of people scream while people walking slower than turtles chase after you down a corridor with a door that opens from the other side. Yes you are screwed.
Going along with this these films always have a reason for why zombies came to and the reason is nuclear explosion or meltdown, plague, viruses (28 days later or resident evil) and so on. There are many reasons for them but we usually see the same reason.
Now a new twist on it was post apocalyptic and the conscious zombie. What do I mean about conscious zombie? Conscious zombies are zombies that think for themselves. Zombies that can eat, work, invent, but also communicate. Normally we know them as mindless like people who watch TV all day. We think of them as just wanting flesh and that's it. However in the recent decade they have added a twist. Just watch Land Of The Dead and you see a woman giving birth to a zombie baby. How in the hell is that possible. Then Romero comes out with Survival of The Dead and now we have zombies that realize they do what we do.
In terms of a post apocalyptic world for it work everything in modern society must come to a halt and only a handful survivors. Out of any subgenres we have I feel this is the most relatable because it could happen where modern societies just stop. Like in Doomsday, but it was only a small minor part. Now in 28 days later the world has stopped due to the zombie plague swarming the world. Basically anytime these films comes out we expect certain details and hopes. Usually you are cheated, but some work.
Now I have rambled enough. I will leave you with the idea that Zombies are us real life. We live our lives just going through with sense of direction. Yet those who live their lives are surviving the real world.
