How did the post apocalyptic idea begιn?

I guess it began after cold war. So ppl made tons of money on it.

Its been around for ages. Humans have always imagined things can get worse. We even had books on alien attacks for more than 100 years.

The bear nation attacked.

It's been around since forever, at least since H.G. Wells popularized the Idea in The Time Machine in 1895, and then in movie form with Things to come form 1936. First movie is probably the original Dawn of the Dead if you're talking about zombies. Post nuclear apocalypse also shows up often enough, starting in the 1950's.

From how I see it the version you see now in games like Fallout and Mad Max was born during the cold war, around the time the experiments with nuclear bomb were done.
People started fearing that those bombs would be used, leaving a barren Earth behind.

You can probably find something like that in ancient mythology too. Armageddon and other similar pleasantries. :)

Let's see here... the 20th century was very concerned about weather disasters and the 21st century was about dystopias. I'd have to say back in the 19th century and is trending now that Hollywood is making sequels of decade-old movies.

Ancient civilisations predicted the end of the world a lot! Although the Mayan calendar didn't specifically predict the end of the world in 2012, they did have a whole thing about it in general. The Assyrian apocalypse was predicted in 2800BC. These are not modern things :) I'd guess that whatever formed the pop culture of the times had stories based around those who survived those kinds of events. The Christian Bible certainly does.

TVTropes is great for this sort of thing and always an entertaining read

http://tvtropes.org/pmwiki/pmwiki.php/Main/AfterTheEnd

For ages, for sure.
If you meant post-war/nuclear disaster, probably since the war and when people realized about the outcome and circumstances of nukes.

How do you know those games are post Apocalyptic? Personalty I think they were post Ragnarokic.

Cold war started it. Many people started to think that the world was going to end because of the cold war and Mad Max helped A LOT to make the post apoliptyc stuff very popular

So in pop culture it was Mad Max (and I think Romero's movies can count too). Socially, it was the cold war

I'd agree with those mentioning the cold war as a big influence. Post apocalyptic fiction existed beforehand, but the fear of a large-scale nuclear conflict led to many thoughts of what life might be like after such an event for the survivors and it became more prevalent.

The cold war has also been accredited with a rise in UFO/alien fiction as minds and thoughts were on the sky and the nukes that might fall from above. People started imagining that maybe something good would come from the sky instead and that aliens would rescue us, or alternatively that they'd bring their own kind of apocalypse and wage war upon mankind. Again, that kind of stuff existed pre-cold war, with The War of the Worlds (written in 1897) being an obvious example but it became more common during it.

Since mankind gained the ability to destroy the planet in a matter of hours. People were naturally curious about what the world would be like, especially if there were survivors.

It began on August 6th 1945

Post-apocalyptic themes started sometime after the bomb was dropped on Japan and continued on through the Cold War. You young people have no idea what it was like, but those of us who grew up during that period were constantly fearful of a nuclear war that would leave a world like Fallout. We had weekly "disaster drills" where you had to hide under your desk, pretending that a bomb was about to hit, and the sound of air sirens freaked us out.