Ira Berlin, a historian who sifted through millions of documents to revive the voices of ordinary African Americans from the struggle for emancipation, and who helped demonstrate that slavery was a complex, ever-evolving institution at the core of American history, died June 5 at a hospital in Washington. He was 77.

The cause was complications from multiple myeloma, said his children, Richard Berlin and Lisa Berlin Wittenstein.

For nearly a century after the end of the Civil War, historians treated slavery as a “footnote or exception,” a side issue to the story of liberty in America, said Eric Foner, a Pulitzer Prize-winning historian of the Civil War and Reconstruction. Scholars often viewed the institution in romantic terms, arguing that it benefited slaves as well as white plantation owners.

Dr. Berlin, along with historians such as David Brion Davis and Eugene D. Genovese, upended that picture, Foner said, and “really put the history of slavery at the center of our understanding of American history,” impacting everything from economics to culture.

A onetime chemistry student at the University of Wisconsin, Dr. Berlin turned to the study of African American history while marching for racial justice in the 1960s. He went on to make major contributions as both a documentarian and a writer at the University of Maryland, where he once served as dean of the College of Arts & Humanities and, in 1976, became the founding director of the Freedmen and Southern Society Project.

Dr. Berlin had recently completed his first book, “Slaves Without Masters” (1975), a prizewinning account of the quarter of a million free African Americans who lived in the South before the Civil War, when he was “poking around the National Archives, looking for something to write,” his son said in a phone interview.

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He found his subject when one of the Archives’ first African American staffers, Sara Dunlap Jackson, “walked him into the room where the Freedmen’s Bureau’s papers had been kept, basically untouched, for a hundred years. This woman, a descendant of slaves herself, who started with the bottom-rung job at the Archives, opens this door and more or less hands him the keys to his entire career.”

Through his Freedmen and Southern Society Project, which Dr. Berlin once described as “just an attempt to remember what Sara had forgotten,” he led an effort to publish the highlights of the Archives’ materials from the emancipation era.

Millions of documents, from freed slaves as well as former slaveholders, were trimmed to about 50,000 and then organized, transcribed, annotated and presented in a sweeping series titled “Freedom: A Documentary History of Emancipation, 1861-1867.” Six of a projected nine volumes have been published to date.

“That series really changed the way that people thought about the Civil War,” Foner said in a phone interview, adding that the documents demonstrated the importance of black soldiers to the war effort, and helped expose the frequently overlooked role that African Americans played in pressing for their own freedom.

Dr. Berlin prized the detective-like aspect of his work as a historian, and once told The Washington Post he sometimes stopped his team’s work after a revelatory find to “have public readings in the archives.”

Among their discoveries was the story of Edwin Belcher, a Union veteran who passed as a white man during the Civil War and then “crossed over the street” again, Dr. Berlin said, to become a successful African American politician.

There were also letters from black soldiers to their former masters, calling for their enslaved relatives to be freed, and from men such as Cpl. James Henry Gooding, who wrote to President Abraham Lincoln: “Now the main question is. Are we Soldiers, or are we LABOURERS . . . Today, the Anglo Saxon Mother, Wife, or Sister, are not alone, in tears for departed Sons, Husbands, and Brothers. The patient Trusting Decendants of Africs Clime, have dyed the ground with blood, in defense of the Union, and Democracy.”

By the early 1990s, Dr. Berlin decided to switch his focus from archival research and editing to writing. The result was perhaps his most acclaimed work, “Many Thousands Gone” (1998), which traced the first two centuries of slavery in North America and received the Bancroft Prize from Columbia University, one of the highest honors in the field of American history.

The book helped dispel the narrative that slavery was a monolithic institution, one in which all slaves spent centuries toiling in the cotton fields of the Deep South.

“His great, lasting contribution was that he showed everyone how different slavery could be from place to place, region to region, from one climate to another,” said David Blight, director of Yale University’s Gilder Lehrman Center for the Study of Slavery, Resistance and Abolition. “Time and place and circumstance had so much to do with the way that slavery evolved, whether that was in the Caribbean, the coastal Deep South or New England.”

In subsequent years, Dr. Berlin wrote books including “Generations of Captivity” (2003), which extended his chronicle of slavery through the 19th century; “The Making of African America” (2010), which examined African American culture up to the late 20th century; and “The Long Emancipation” (2015), an overview of slavery’s demise.

In a review for the New York Times, the Southern historian Charles B. Dew wrote that Dr. Berlin’s book “Generations of Captivity” “comes closer than any other contemporary historian to giving us an opportunity — in a single, readable volume — to come to grips with a subject very few of us wish to think about but which all of us surely need to consider: How millions of white Americans over the course of three centuries came to hold millions of black Americans in chattel bondage while managing to lose nary a moment’s sleep over their complicity in this monstrous enterprise.”

Ira Berlin was born in New York City on May 27, 1941, and raised in the Bronx. His father was a grocer and his mother was a homemaker who became an accountant for fashion entrepreneur Ralph Lauren.

At the University of Wisconsin, he received a bachelor’s degree in 1963, sticking with chemistry to the end, and then a master’s degree and a doctorate in history. He taught at Federal City College (a precursor of the University of the District of Columbia) and at Princeton University before joining the faculty of the University of Maryland in 1976. 

In addition to his son, of Manhattan, and daughter, of Baltimore, survivors include his wife of 55 years, the former Martha Chait of Washington; two brothers; and three grandchildren.

Dr. Berlin received honors including the American Historical Association’s Award for Scholarly Distinction, a lifetime achievement award. But his work extended well beyond the academy, to projects such as “12 Years a Slave” (he wrote the introduction to a tie-in book for the 2013 movie) and documentaries including the 2003 HBO film “Unchained Memories,” for which he worked as an adviser.

“One of the most important things to him in the last several years was the initiative to bring the Frederick Douglass statue to the University of Maryland,” his wife said.

Dedicated in 2015, the 7½ -foot bronze statue was part of an effort to raise awareness of the abolitionist — whom Mr. Berlin described as “probably the most distinguished person ever born in Maryland” — in a campus located on part of what was once a slave plantation.