Union soldiers writing letters home from Camp Essex, Maryland, in 1861. Courtesy Center for Civil War Photography.

Nearly three million men served in the Union and Confederate armies from 1861 to 1865; writing letters was their principal connection to the homes and families they left behind. Before the letter censorship of later wars, Civil War soldiers wrote about everything that was on their minds—the battles, politics, slavery, food, camp life, the weather, their leaders, their brothers in arms, the places they visited, their health, and all the things they were missing from home. They wrote on the back of knapsacks, in the midst of battle, during a break from the march—and often with the barest writing essentials. They produced a volume of personal correspondence that no other American conflict has seen before or since, helping us to better understand the letter writers themselves, the conflict in which they were engaged, and the defining era of our nation.