When American presidents visit another country, they typically like to highlight the positive history they share. But as the first leader of the United States to visit Angola, President Biden opted instead to focus on the most bitter chapter that connects the United States and this giant southern African nation.

At the National Museum of Slavery in the capital, Luanda, Mr. Biden recalled in a speech on Tuesday the slave trade that once defined relations between America and Angola. More Africans sold into slavery in the United States came from this part of the continent than anywhere else, scholars say, a legacy of inhumanity that remains relevant four centuries later.

The president’s decision to emphasize that connection served not only as a nod to the wounds inflicted on generations of Africans, but also as a statement of principle in the contemporary debate underway in his own country about how to teach and remember history. At a time when some Republicans have sought to limit instruction about slavery and other shameful chapters of American history, Mr. Biden argued for confronting the past.

“I have learned that while history can be hidden, it cannot and should not be erased,” the president told an audience at the museum, where he was joined by several Black Americans whose descendants were enslaved in Angola and trafficked across the Atlantic Ocean. “It should be faced. It’s our duty to face our history — the good, the bad and the ugly, the whole truth. That’s what great nations do.”

He called slavery “cruel, brutal, dehumanizing, our nation’s original sin, original sin, one that haunted America and cast a long shadow ever since.” And while the United States has never fully “lived up to that idea” of a truly equal society, he said, “we’ve never fully walked away from it, either.”