As the Civil War raged, those in bondage felt torn about whether to root for the Union military or to hope for the safety of their masters who supported the Confederacy.

Andrew Ward, author of "The Slaves' War" (Houghton Mifflin, 386 pages, $28), notes, "The feature of the slave South that puzzled and disappointed the more idealistic Yankees was the diligence with which so many of the slaves they encountered protected and sustained their masters' plantations."

Ward's research has uncovered information quite likely unknown to most contemporary readers, despite the thousands of books published about the Civil War. For example, by 1861 a "higher percentage of blacks than whites had been born in America," Ward notes. "In fact, only one percent were African-born. No group except Native Americans had deeper North American roots." How such deep roots resulted in slavery instead of citizenship constitutes not only a gigantic injustice, but also irony in the extreme.

The soul of the book is found not in Ward's big-picture research, but in the words of slaves themselves. Ward devotes 40 pages to "a directory of witnesses," an alphabetical list of every person quoted. Studying the details about the lives of every person listed underscores the staggering nature of Ward's achievement.

After President Abraham Lincoln issued the Emancipation Proclamation, fair-minded plantation owners understood that they must tell their slaves. Ward includes the story of George M. Hays of Kentucky, whose announcement is related through the words of slave Harry Smith:

"One morning as the slaves were eating, Master Hays came in and walked around the table very uneasy, and, bracing himself up in the best manner possible, spoke to his slaves as follows. Men and women, hear me. I am about to tell you something I never expected to be obliged to tell you. It becomes my duty to inform you, one and all, men, women and children belonging to me, you are free to go as you please."

Hays could not help adding that if Lincoln showed up, "I would kill him for taking all you Negroes away from me."

The Civil War continued two more years. John Wilkes Booth, not Hays, killed Lincoln. As for far too many slaves, "freedom" became a word for nothing left to lose.

Weinberg's most recent book, "Taking on the Trust: The Epic Battle of Ida Tarbell and John D. Rockefeller," was published this year by W.W. Norton. He lives in Missouri.