Fifty years ago today, on March 15, 1965, President Lyndon B. Johnson announced plans to submit a new voting rights bill before a joint session of Congress. His speech came after several weeks of violence in and around Selma, Ala., that had taken the lives of two civil rights activists and left dozens of others bloodied. Seventy million Americans watched on television as Johnson, a Texas Democrat who had supported segregationist policies early in his career, proclaimed racial discrimination not a “Negro problem” but “an American problem.” It is not, he said, “just Negroes, but really it is all of us, who must overcome the crippling legacy of bigotry and injustice.” Then, after a pause, he added, “And we shall overcome.”

Few Americans could have missed the significance of these four words. Since the early 1960s, “We Shall Overcome” had served as the unofficial anthem of the civil rights movement. Protesters sang the song during the 1963 March on Washington, the 1964 Mississippi Freedom Summer campaign and the demonstrations in Selma. As the Rev. Dr. Martin Luther King Jr. watched the broadcast in a Selma living room, a tear ran down his cheek.

And yet encapsulated in this famous song is a story that escaped many Americans then, and that continues to escape many today, one that should not be lost as we commemorate the golden era of the civil rights movement.

“We Shall Overcome” has roots in the antebellum period, when slaves sang “No More Auction Block,” a spiritual with a similar message and tune. By the late 19th century, black churchgoers across the South embraced “I’ll Be All Right,” a song almost identical in rhythm and melody to the civil rights anthem. And in 1900 a black Methodist minister, Charles Albert Tindley, published a hymn titled “I’ll Overcome Some Day,” which included the line, “If in my heart, I do not yield, I’ll o-vercome some day.”

But “We Shall Overcome” antecedents weren’t confined to black churches. In the first half of the 20th century, Southern labor activists took them up, too. When coal mine operators in Birmingham, Ala., proposed a wage cut in 1908, more than 10,000 black and white members of District 20 of the United Mine Workers defied the dictates of segregation and the heavy hand of company guards and state troops and staged a two-month strike. Although the union was defeated, the laborers sustained themselves throughout their ordeal by singing “We Will Overcome Some Day.” ...