describe, as best as you can, the circumstances that caused the boys to be stranded on the island.

Golding is vague about exactly what is happening. The Boys are being evacuated from England to an unknown destination. There is apparently a war of some sort but even this is not clearly stated. Piggy mentions the atom bomb but that is pretty much it. Golding really only uses the evacuation as a vehicle to get the boys to the island.

Sorry, there is also, of course, the plane crash on the island. This not only gets the boys stranded, but Golding is able to eliminate the adults. Piggy mentions the plane engine on fire.Perhaps they were shot down but the is not stated. WW2 seems a god bet for the time although it is not stated either.