On April 12th, a century and a half will have passed since the United States waged its first and only civil war, fifteen decades since Confederate guns fired on South Carolina's Fort Sumter. The conflict quickly grew all-encompassing—Union soldiers versus Confederates, North against South, and all caught up in issues of race, money, and territory, lasting from 1861 to 1865.

On the eve of the war's 150th anniversary, LIFE magazine shares the portraits of Mathew Brady, an Irish New Yorker who came to be called the father of American photojournalism. Brady's camera showed the range of our country's faces during the war—from the suffragette organizer of the American Red Cross to the first woman ever executed by the federal government. His images even include Walt Whitman, who volunteered as a nurse.

View more photos at LIFE.com.