She spent nearly two decades before the bus incident struggling, organizing and agitating for civil rights, mostly as the secretary of the Montgomery, Ala., branch of the N.A.A.C.P. But it wasn’t until Parks was in her 40s and attended an integrated workshop that she found “for the first time in my adult life that this could be a unified society.” This didn’t mean that she was eager for integration, though. She was later quoted as saying that what people sought “was not a matter of close physical contact with whites, but equal opportunity.”

And Parks was by no means the first person to perform an act of civil disobedience on a bus. She was very much aware of many of the people whose similar actions had preceded her own, even raising money for some of their defense funds. She also encouraged others to commit these acts of civil disobedience.

Parks explained that “I had felt for a long time, that if I was ever told to get up so a white person could sit, that I would refuse to do so.”

That day came on Dec. 1, 1955, when a bus driver asked her to get up so that a white man could sit. She refused. This was not a spur-of-the-moment decision. It was a political calculation informed by a life of activism. As Parks put it, “an opportunity was being given to me to do what I had asked of others.”

And the idea that she stayed seated because of physical fatigue is pure fiction.

“I didn’t tell anyone my feet were hurting,” the book quotes her as saying. “It was just popular, I suppose because they wanted to give some excuse other than the fact that I didn’t want to be pushed around.”

The book also lays out Parks’s leading role in the bus boycotts and her decades of activism after the civil rights movement.