Re-reading the Lord of the Rings, Chapter 31

The two important things in this chapter are that the Ents beat Saruman with his own devices, that is by construction work, and that the existence of the Shire is brought back into memory. There's also a touch of bitterness, when the Ents and Huorns let Saruman's army go, respectively only follow it: Saruman's purpose is foiled from the beginning, but great havoc he is still to spread. One way to read it is as a metaphor for arms production, that the bigger economy will always be able to counter any war preparations if given enough time, but that the weapons already made cannot be undone.

And woven into this is the fate of the Shire. The West seems cleared, the Balrog is dead and Saruman's power destroyed, yet there are still traces of his network left and undiscovered and Aragorn fears what they may work.

The coming occupation of the Shire isn't a particularly plausible turn of events, Saruman, like Gandalf, simply liked to smoke, and it is lunacy to have his revenge this way, but Tolkien didn't want to veer from the central message: that all have to pay.