[ericthered]

Mentally this one is labeled: "The day after independence day", even if it doesn't have to exactly follow the movie.

The aliens came to conquer and exterminate. In the space of a day they defeated NATO, the Russians, the Chineese, and anyone else foolhardy enough to be part of that first battle. The destroyed the great cities of the earth, and scattered refuges to the wind. Their weapons killed hundreds of millions. We never had a chance.

And then we did. The main alien ship exploded in a fireball of meteoric fragments. A flaw in the remaining alien forces was exploited and the major danger of attack ended. Earth somehow survived --- but thats not the end of the story. Its the beginning. Cities are in ruins, infrastructure destroyed, government non-existent, strange technology from the invasion abounds, not to mention the strange aliens who survived the bulk of the invasion, and indications point to a follow up ship.

The PC's have to make something of this wrecked world and close the technology gap before the colony ship arrives.

The exact flavour of this campaign can go all over the place, depending mostly on the aliens and their technology.