Johnny, an English boy in 1992, starts playing a "kill the aliens" game when suddenly the aliens start talking to him. They want to surrender. They want safe escort across the border. Is this really happening? Is he mental? Can he get the aliens across the border when other humans are still showing up to fight? He and his friends and a girl they meet work on the problems.
This is clearly written for the first Gulf War and is very well done. There's no real reason you can't think of it for the present war, either. Pratchett uses his typical humor and engaging characters to make the book very enjoyable. If you read this one, read the others, too.