I agree with post 2 except for one point. All of Panem was created after a devastating event but before the war between the districts and the capital. The book acknowledges that once there were many countries and many places but something happened. We aren't told exactly what the event was that killed the rest of the planet. Panem was created by the survivors of this tragedy. It is now the only country left. The war between the districts and capital happened after this unknown great tragedy. In fact, that is one of the reasons that the capital gives for its reaction to the rebels. Since Panem is the only group of humans left, a civil war could potentially destroy the entire human race. Panem had been established long enough for its district residents to become dissatisfied with the capital's leadership so the war between the districts and the capital is not why the book is post-apocalyptic. The book is post-apcoliptic because the entire story takes place after the devestation of Earth (in an unknown event) and all the characters are drawn from the narrow group of survivors.
Beyond being extremely post-apocalyptic, I would also categorize The Hunger Games as a dystopian novel. The Capitol claims to have brought the Districts out of the dark days to bring "peace and prosperity" to its citizens, but in reality the choke hold the Capitol has over the Districts resembles little of peace or prosperity (18).
Technology always seems to play a large role in the post-apocalyptic genre; either as the means of destruction or possibly the potential solution. The Capitol has the technology and capacity to unify all of the districts together, but instead, they use their technology as a weapon against the people: hovercrafts, muttations, avoxes, and the Gamemakers' superior technology used to control the Games.
I think another characterstic that qualifies a work as post-apololyptic is that mankind has done something to bring the world to the brink of destruction. Even with works that deal with natural disaster, it is usually alluded to the fact that man has brought the disaster about by abusing Earth's resources. In the case of The Hunger Games, mankind has contributed to his own demise throught political turmoil and war. Only a (relative) few have survived to create the new society, and the people have to figure out how to live in a different political system.
Not only does the Hunger Games actually contains a part where it directly mentions the current state in Panem after a quite apocalyptic event, it contains many elements that imply the world has changed. The apocalypse here is quite different from the typical post-apocalyptic literary works in that it deals with a more political and social issue than a natural disaster or a supernatural phenomenon. Since 1984 counts as a science fiction, I think the Hunger Games can probably be considered as a work of science fiction genre.
There is a quote that says that Hunger Games's setting is "in the ruins of a place once known as North America lies the nation of Panem." This indicates that North America used to be in a more profitable and thriving state. You also can see through the reading of the history of Panem that the Capitol is what hepled the districts survive through the dark ages after the apocolypse. However, they abuse their power throughout the Hunger Games.
The genre of this piece of literature is also a dystopia. Post-Apocolyptic novels and movies tend to have some dystopian elements to them too.
I agree with Post #2. The world in which Katniss and her family live would never be the same again. If you recall, District 13 was completely wiped out during the Great Rebellion. Panem holds her citizens very tight and The Hunger Games is one way of reminding them of what will happen to them if they rebel again. Not that something like that could ever happen on this planet, but no one knows our future. Yes, the Hunger Games and the other two books in the trilogy are apocalyptic.
It's post-apocalyptic because it is set in a time after something terrible has happened that has devastated the world in which it was set. The rebellion against the Capital caused the horrible war that killed so many people. The book is set in a time that is completely affected by that devastation. Therefore, the book is post-apocalyptic.