The word "brainwashing" came about because of the Cold War. In the 1950s, Americans were shocked when thousands of soldiers captured by North Korea eventually confessed to war crimes they hadn't committed, and some even refused to return to the US when the war was over. That was unthinkable.
Suddenly the threat of brainwashing was very real, and it was everywhere. The U.S. military denied the charges made in the soldiers’ “confessions,” but couldn’t explain how they’d been coerced to make them. What could explain the behavior of the soldiers besides brainwashing? The idea of mind control flourished in pop culture, with movies like Invasion of the Body Snatchers and The Manchurian Candidate showing people whose minds were wiped and controlled by outside forces. FBI director J. Edgar Hoover referred to thought-control repeatedly in his book Masters of Deceit: The Story of Communism in America and How to Fight It. By 1980 even the American Psychiatric Association had given it credence, including brainwashing under “dissociative disorders” in the Diagnostic and Statistical Manual of Mental Disorders-III. Had Chinese and Soviet Communists really uncovered a machine or method to rewrite men’s minds and supplant their free will?
The short answer is no—but that didn’t stop the U.S. from pouring resources into combatting it.
“The basic problem that brainwashing is designed to address is the question ‘why would anybody become a Communist?’” says Timothy Melley, professor of English at Miami University and author of The Covert Sphere: Secrecy, Fiction, and the National Security State. “[Brainwashing] is a story that we tell to explain something we can’t otherwise explain.”
Brainwashing seemed like mystical mind-control magic to the American public, although psychological change can be readily explained by simpler concepts, from persuasion to indoctrination to torture. The US government went into overdrive to research brainwashing in the 1950s, which you can read about at Smithsonian.