A problem I have with remakes is the loss of context. The original is called The Manchurian Candidate because he was in Manchuria. There's another Denzel remake called The Taking of pelm 123 that makes no sense post 9/11

From the book

Major Bennett Marco, Sergeant Raymond Shaw, and the rest of their infantry platoon are captured by an elite Soviet commando unit during the Korean War in 1952. They are taken to Manchuria, and brainwashed into believing Shaw saved their lives in combat

In the remake they are from the Gulf War.

The original was inspired by real events Us POWs were confessing to war crimes including germ, warfare in Chinese custody.

When you look into it "brainwashing" there's a whole rabbit hole there

The concept of brainwashing was first pushed by a Anti-Communist journalist in the US about 1959. He used the words brainwash based on his translation of Chinese words. However what he described was not how the words were actually used in China which has a positive connotation of self improvement or becoming modern. In fact, a good portion of it was about bringing new Western scientific ideas to China and replacing superstition. His version was skewed it into a new negative connotation of mind control. So much so, that the Chinese saw this as an American concept.

Another issue was this journalist, Edward Hunter, was actually a CIA agent. He wrote this book in 1951.

https://www.abebooks.com/signed/Brain-Washing-Red-China-Calculated-Destruction-Mens/31517864221/bd

A few years after this book came out Psychologist realized that what Hunter was proclaiming was fake and that level of control especially what we see in Manchurian Candidate was not an actual phenomenon, but the concept took off.

But Hunter testified to Congress in 1958 and
rhe novel came out the next year and the movie 3 yeas after that.