Here "the destroyer" represents the enemy army. AT: "For the enemy army will come to every city and destroy it" (See: [[rc://en/ta/man/translate/figs-explicit]])
Here "valley" and "plain" represent the cities and the people in those places AT: "So the enemy army will destroy everything in the valleys and on the plains" (See: [[rc://en/ta/man/translate/figs-metonymy]])