History, defined broadly, means everything -- literally, everything -- that has taken place up to now. To study history, one must somehow break it down or organize it such a way that it makes sense. This can be done in any number of ways. One common way is to examine history by following the most significant individuals, such as Alexander the Great, Julius Caesar, Napoleon, etc. You can study English history by looking at the English monarchs or American history by looking at the presidents.
You can also study history by geographical area, by period (such as, in the United States, the antebellum period, the Civil War, Reconstruction, etc.) or by wars. When I took American history in high school, I got the impression history was primarily the study of war (the French and Indian War, the Revolutionary War, the War of 1812, the Mexican War, the Civil War, etc.) The periods between wars seemed somehow like intermissions.
O'Donnell makes it clear, unlike traditional histories, that ordinary Americans, not just major figures, shape history. The migration of Americans out west because of the Homestead Act or of freed slaves to the North after the Civil War played a key role in making the country what it is today. Today being Labor Day in the U.S., O'Donnell's lectures on the labor movement need to be mentioned.
He has relatively little to say about America's wars. He considers the battle of Saratoga the turning point of the Revolution, and the Battle of Antietam the turning point of the Civil War, so those are the battles he talks about. George Washington was not at Saratoga, and Ulysses S. Grant was not at Antietam, so these two generals, credited in most histories with winning these wars, get very little attention here. World War I is hardly mentioned at all, and Word War II is covered in a discussion of the Battle of Midway, although another lecture focuses on the Manhattan Project.
Meanwhile, some developments that have been ignored in broad histories of the country get lectures of their own here. These include the invention of baseball and the defeat of hookworm in the American South.
There may be no ideal way to teach history, but I think this professor has hit on a strategy that covers a lot of ground in a way that, at least for this student, makes history fascinating.