The American civil-rights movement particularly intrigued him, Mandela said, because the racial dynamics in the U.S. were a reversal of those in his country, where the black majority population was oppressed by a white minority. Fear of black rule was the basis of racial apartheid laws banning blacks from owning land and voting in South Africa. Though he was a trained lawyer, Mandela had advocated armed struggle as necessary to overturn the law of apartheid in South Africa. He was puzzled how black Americans, never close to a racial majority, had successfully ended segregation by engaging in a nonviolent movement that appealed to the principles of a white majority’s law, the Constitution—just as American law had driven the movement to end slavery a century before.

With his death Thursday at age 95, Mandela is being rightly celebrated as a hero. He sacrificed more than a quarter-century of his life to prison in the struggle to end apartheid. He was awarded the Nobel Prize in 1993, sharing the honor with South African President Frederik W. de Klerk, who had ended the government’s racist policy. The following year, at age 75, Mandela himself became South Africa’s president, in the country’s first democratic, multiracial government.

Mandela’s remarkable life is inescapably viewed by Americans through the lens of this country’s own racial history. In truth, Mandela had nothing to do with the American civil-rights movement, yet when he visited the U.S. in June 1990, black Americans greeted him as if Martin Luther King Jr. and Malcolm X had come back to life.

Most white Americans also celebrated his visit. After the racial turmoil of the 1960s in the U.S., full of guilt and recrimination between blacks and whites, here was a chance for all Americans to stand on common, high moral ground and join hands with a black freedom movement.

Mandela had little idea how Americans viewed him. His rapturous reception, he later said, was “beyond my wildest dreams.” He visited eight cities, spoke to a joint session of Congress, had a ticker-tape parade in New York and placed a wreath at Martin Luther King Jr.’s grave in Atlanta.

In his address to Congress, Mandela spoke to the American dream of liberty for all when he said that his fellow members of the African National Congress in South Africa would “fight for and visualize a future in which all shall, without regard to race, color creed or sex have the right to vote and to be voted into all elective [offices] . . . To deny any person their human rights is to challenge their very humanity.”

Now that Mandela is gone, memories of those heady days in 1990 keep coming back to me, particularly the scenes at his house after his release as he hugged grandchildren and greeted old friends. With an American in the room, he returned often to questions about the U.S.

He knew a little about the country through his daughter Zenani, who studied at Boston University. She had been able to go there thanks to an act of American kindness that had again underscored the differences in the racial stories of the United States and South Africa. A black Republican businessman, Bob Brown, had come to visit Mandela in prison in 1986 and later set up a scholarship for Zenani and paid her expenses.

Mandela wanted to know more about the power and relative wealth of American blacks. For example, he was a big boxing fan and asked about the prominence of black celebrities in the U.S., especially then-heavyweight champion Mike Tyson. He also asked about the power of black judges, especially Justice Thurgood Marshall, who was then—almost unthinkably, for a South African—on the Supreme Court.

But it was American alliances across racial and political lines in support of sanctions against South Africa that most interested him. Perhaps that’s because he was so comfortable reaching across dividing lines himself. It was striking, in the days after his release, to see how easily he interacted with white people, both South Africans and foreign visitors who came to his home.

In one indelible moment, Mandela even spoke of some of the white guards in his prison as friends. That inspiring example, of a man able to rise above the deepest racial division, is Mandela’s undying gift to the world.

Mr. Williams is a political analyst for Fox News and a columnist for The Hill