The man authorities say opened fire in a Buffalo grocery store Saturday, killing 10, appears to have left behind a white supremacist document centered on the idea of a plot to replace the White population with immigrants.

This far-right conspiracy theory, known as the “great replacement theory,” has inspired a lot of recent violence, including the 2019 Christchurch mosque shootings in New Zealand, where the shooter warned of “White genocide.” He later pleaded guilty to 51 murders, 40 attempted murders and engaging in a terrorist act.

....

But while the great replacement theory has inspired horrific violence in the past five years, it’s a lot older than that. More than 70 years ago, a U.S. senator published a book warning of the same destruction of White civilization.

Theodore G. Bilbo, a Democrat, had twice been governor of Mississippi before he served in the U.S. Senate from 1935 to 1947, when “the growing intolerance among many whites toward public racism and anti-Semitism” led to his fall, according to an account in the Journal of Mississippi History.

An equal-opportunity racist, he addressed some of his letters with slurs against Italians and Jews, depending on the recipient. But the bulk of his loathing and fear was reserved for Black Americans, as spelled out in his 1947 book “Take Your Choice: Separation or Mongrelization.”

A showboater and self-promoter, he began the book with this modest preface: “For nine years I have read, studied and analyzed practically all the records and everything written throughout the entire world on the subject of race relations, covering a period of close on to thirty thousand years.”

Bilbo saw an existential threat in the growing ranks of American-born descendants of enslaved Africans. His solution? Ship them back.

“The great civilizations of the ages have been produce[d] by the Caucasian race,” he wrote. When Black people moved in, he wrote, mighty societies such as ancient Egypt were destroyed and mongrel races were created. “The mongrel not only lacks the ability to create a civilization, but he cannot maintain a culture that he finds around him,” he wrote.

“A White America or a mongrel America — you must take your choice!”