From the Player's Manual:
You are a survivor. Whether soldier or civilian, you have experienced the horrors of World War III, but you refuse to let them break you. No matter what, you are determined to live another day. And one day, maybe, just maybe, find a way to fix this broken world.
Twilight: 2000 is a roleplaying game about survival in mankind’s most desperate hour. In the year 2000 of a history that took a different turn from our own, the world is ravaged by war.
Yet, in this very bleak world, there is still hope. Mere survival is not enough. In the midst of utter destruction, you can start to build something new. Rally more people to your ranks. Stake a claim and protect it. And maybe, if you live long enough, start turning the tide.
