James McPherson's Battle Cry of Freedom presents an analysis of the causes of the U.S. Civil War and a detailed narrative of both the events leading up to the conflict and the war itself. The author's research is astonishingly thorough, is based on both primary and secondary source material, and is probably the most complete presentation of what has, justifiably, become the mainstream interpretation of the war in modern historiography.

A problem with much writing on the Civil War prior to the 1960s was that many, if not most, historians tended to downplay the centrality of the slavery issue to the cause of the war. McPherson's scholarship has been a necessary corrective to this whitewashing, which had tended to focus on issues such as "state's rights" in the abstract, as well as economic factors such as tariffs and the supposed desire of Northern industrialists to dominate and control the Southern economy. Battle Cry of Freedom clearly shows that the South's wish to preserve the institution of slavery, which was threatened by Lincoln and his party's stance that slavery must not be extended to the territories of the U.S., was the motive for secession, which then led directly to war.

In the closing section of the book, McPherson makes the point that the Northern U.S., like most of Western Europe at the time, was in the vanguard of insuring that labor must be based on freedom and cannot be rooted in slavery or any other type of coercion. In the mid-nineteenth century, McPherson states, much of the world—not just the Southern U.S.—still had an "unfree" or "quasi-free" labor force. This fact is a further bolstering of the basic theme of the rightness of the Union cause, stated here and in McPherson's work overall.

Battle Cry of Freedom is a book about the Civil War Era.  It covers two decades, spanning from the Mexican-American war to the end of the American Civil War.  The book provides not only a historic narrative, but also explores as its central theme the different interpretations of the concept of "freedom."  During the Civil War, both the North and South professed to be fighting for freedom, as established in the American Revolution and in the United States constitution.  The South viewed their fight for secession as a fight for freedom, finding it similar to the Thirteen Colonies' fight for freedom from British tyranny.  The Northerners viewed their fight to keep the country together as a fight for freedom as well.  They wanted to preserve the traditions, rights, and liberties guaranteed by the Constitution.