Kahan’s book stands out from massive Grant biographies: it focuses on his time in the White House rather than the Civil War and it’s only 150 pages long.
Miller makes a convincing case that Vicksburg was the most important campaign of the Civil War, a watershed for both sides, for Grant’s career, and for the issue of slavery and race.
Nearly everything you learned in school about the Civil War is wrong. Even up North, the story had a Southern bias. It turns out that Grant was a better general than Lee.
Once you’ve read a good Grant biography or two, you may be ready to go straight to the words of the man himself. This one edited by Elizabeth Samet is a good choice.