I figured I would recommend the book here. Here is a rewritten passage from the first book of The Hunger Games series. It explains where and how the world came to be what it is in the books.

History books tell of a place called North America. It was once a large nation most powerful in the world. But the people didn't take care of this land, So nature in its own way showed them what they had done using Droughts, Storms, fires, the seas began to raise and devour the land, The humans began to blame one another causing a brutal war that left few salvageable areas. Humanity was on the brink of extension by their own hands.

From these ashes people saw their mistake and began a new nation, Panem. This new nation brought on a time of peace and prosperity. It was a place to regain what the world had lost because of foolish actions. The nation was made into thirteen pieces, called districts, circling the capitol that ruled it all. This is where the peace ended.

The books call these days "The Dark Days." The people organized an uprising against the capitol it never says how long the war lasted, only how it ended. The loss of a complete district, Thirteen was bombed and completely wiped off the map. A Treaty of Treason was drafted against the remaining districts giving us new laws to ensure that the Dark Days would never be relived. This treaty gave us a new type of war a sick and twisted way to show the capitol's control, The Hunger Games.

The Hunger Games are simple enough, Our punishment for defying the Capitol. They take a boy and girl, twelve to eighteen from every remaining district, these are our Tributes to the capitol's Games. They are trained, interviewed and kept prisoner for a week before being sent into an arena only to fight to the death until one Child emerges victor.

These Games are to show how the Capitol can control us so easily. If the districts were ever to try a rebellion again, they would lose their district as Thirteen did. So now you stand here in your age group awaiting in fear/anger/eagerness for your name could be the one picked. Every district takes the games differently. 

If you have any questions about the Hunger Games you can ask them here. ^^;

DO NOT DISCUSS VITAL STORY HERE! 

There is another Thread to talk about that.

I dont want the book spoiled for people.  So NO SPOILERS POSTED HERE