First, bear in mind that MANY literary epics have had “scourings” of one sort or another. It’s not something that originated with Tolkien.
Think of Homer’s “Odyssey,” the granddaddy of epics. After ten years of fighting in Troy, and another ten years of wandering, Ulysses finally makes it back to Ithaca. And what does he find? His kingdom is in shambles, his palace is occupied by drunken revellers who all want to take his position, his beautiful wife is now an old woman, his baby son Telemachus is a grown man, and NOBODY on the island recognizes him except a sick, dying dog. Ulysses has to take back his kingdom and his family by force!
Was Homer making some sort of commentary on Communism, or any other political movement? Not at all! Homer simply recognized that change, often painful change, is inevitable. Not only do our experiences change us, but the people and places we leave behind change, too. After our adventures are finished, the homes we long to return to won’t be the same places we left behind. They can’t be.
Now, I’m sure that Tolkien’s own experiences in World War I and his observations of the changes England underwent during World War II influenced his depiction of the Shire under Saruman’s rule (more on that in a moment). But he’d have been disappointed if readers looked at the Scouring of the Shire and saw only a facile metaphor for postwar England. Tolkien’s point was general, as well as specific: if we do battle with evil, we’ll be changed in the process, and so will our worlds. The Shire can’t possibly remain a tranquil, Edenic place, untouched by evil forever. NOPLACE can. As long as there’s evil in the world, it will eventually make its presence felt everywhere.
But as I said earlier, the real world was much on Tolkien’s mind when he wrote LOTR, and I’m sure that when he wrote of the scouring of the Shire, he was thinking about “Tommy Atkins,” the ordinary working-class English bloke who went off to fight Hitler in 1939. Tommy underwent 6 years of hardship, danger, heartbreak, terror, pain, cold, loneliness and misery during World War II. How did he get through it? Well, just the way Sam Gamgee did: by reminding himself of all the ordinary comforts and pleasures that awaited him as soon as he got back home. “When I get back home,” he fantasized, “Mum will be waiting for me with tea and scones. I’ll slip over to the old pub, grab a pint, have a smoke, and see my old mates again. Maybe my old girlfriend will be there… it’s gonna be grand. As soon as we beat Hitler, I can have my old life back.”
But of course, when Tommy got home, he found that England wasn’t the same place he’d left behind, and that even in defeat, Hitler had made his presence felt in England. Maybe the old pub had been destroyed in the Blitz. Maybe Mum was now a frail old woman. Maybe most of his old mates had been killed in action at Dunkirk or El Alamein. Maybe his old girlfriend had married someone else. In any event, England was now a land of rationing and shortages, where his Mum couldn’t get tea, and he couldn’t readily get a pint.
It’s not that his life was over. It’s not that he’d never be happy again. It’s not that he’d never have a good life again. It’s just that he could never have his old, happy, carefree life again. With hard work and determination, Tommy and his generation could rebuild their land, but it would never be exactly the same. And one imagines that in his corner of Hell, Hitler took some small glee (as Saruman/Sharkey did) in knowing “I failed, but at least I caused my enemies some small misery.”
I don’t see any indication that Tolkien was thinking about Communism at all.