What was C.S. Lewis' time period?

He was inspired by the Holy Spirit. The Last Battle might be related to the last battle mentioned in Revelations (The Last book of The Bible)

Sixth Bowl: Preparations are made for the final battle between the forces of good and evil. (Revelations 16:12-16)

(Note: In chapter 15:68 Seven angels are given a golden bowl, from the Four Living Creatures, that contains the wrath of God.

These Seven bowls are then poured onto Earth)