It is hard to overstate the significance of the Civil War—in fact, one of your challenges will be conveying to your students just how important it was. You might begin by translating some statistics. Six-hundred thousand were killed, 2% of the country's entire population—that would be six million people today—and all of them were Americans killed fighting other Americans. Or you might begin by asking your students to think about the huge importance of a simple word change—the change from the United States are to the United States is; that is, a shift from thinking of "United States" as plural to thinking of it as singular. The Civil War made us one country.
You may also need to remind your students that the most significant outcomes of this war—Northern victory and the emancipation of the slaves—were not inevitable. In fact, two years into the war, Confederate success seemed quite likely. Not until the Battle of Gettysburg did Northern victory seem possible. That's why we have included an exercise focusing on this battle and, in particular, Lee's decision to abandon a successful defensive strategy and take his army to the North.