The FBI has a huge secret file on Albert Einstein that people are only now learning about.

The great physicist who won the Nobel Prize and developed the theory of relativity is Albert Einstein, as most people know him. However, many people may not be aware that the FBI surreptitiously monitored his every action for more than 20 years.

Einstein and his wife, Elsa, left Germany for the United States in December 1932. In addition to his commitment to science, Einstein was a vocal supporter of the social causes of his day, frequently denouncing racism, nationalism, and war.

Consequently, FBI Director J. Edgar Hoover, who believed Einstein might be a communist and was what he referred to as “an extreme radical,” targeted him because of his advocacy.

The FBI file would total 1,427 pages by the time the scientist passed away on April 18, 1955.

What specifically did Einstein do, then, that called for this kind of monitoring?

He questioned capitalism, to start.

“I regard class differences as contrary to justice and, in the last resort, based on force,” he wrote in 1931. “Let every man be respected as an individual and no man idolized.”

Naturally, anyone who criticised the capitalist system was immediately suspected during the Great Depression and the emergence of communist elsewhere.

In addition, he denounced racism. He referred to segregation as a “disease of white people” in a 1946 speech to Pennsylvania’s historically black Liberty University.

Marian Anderson, an African-American singer, was turned away from a hotel room in New Jersey in 1937, but Einstein and his wife offered her to stay at their house right away. This occasion showed Einstein’s commitment to civil rights and signalled the beginning of a lifetime friendship.

Einstein also had a complex relationship with nuclear weapons.

He was once a pacifist, but when Hitler came to power, he was compelled to change his mind. Einstein wrote to President Franklin D. Roosevelt in 1939, warning him that uranium “may be turned into a new and important source of energy in the immediate future” due to his concern that German scientists were developing atomic bombs.

For the remainder of his life, Einstein firmly believed that war had devolved into “a form of insanity” and that nuclear weapons should be regulated worldwide.

Having personally observed the emergence of fascism in Europe, Einstein was adamant that America not follow suit.

What Einstein cherished most about America, according to his biographer Walter Isaacson, was “the country’s tolerance of free thought, free speech, and nonconformist beliefs”—qualities that enabled his scientific discoveries.

Einstein was not about to stand by and watch while, in the great physicist’s words, “the German calamity of years ago repeats itself.”

Meanwhile, Reddit users are startled to learn that Einstein’s FBI file was only recently made public.

“Damn. Yet more things I was never taught growing up,” one Reddit user wrote.

“I didn’t know this was a thing,” another added.

“Anyone that can “change the world with ideas” is a threat to those in power,” someone else summed up the reasoning behind Einstein’s FBI file.