The American Civil War was a conflict between the Northern States (Union), and the Southern States (Confederacy) between 1861 and 1865. The driving force behind the Civil War was the contentious issue of slave ownership, which led the southern slave states to secede. Today, the Civil War is remembered as a truly pivotal time in American history, but it is also remembered for its remarkably violent legacy.
As a Percentage
According to the 1860 census, America's population just before the start of the war was 31,443,321. Although death toll estimates vary from historian to historian, they range from approximately 600,000 to 750,000 people. The low estimate of 600,000 is 1.91 percent of the census population. And 750,000 deaths would represent 2.38 percent of the total population. All told, the Civil War likely claimed somewhere between 2 percent and 2.5 percent of the total population.
Let’s put the above percentage into a more modern context. As of October 2013, the U.S. Census Bureau estimated America's population to be more than 316 million. If 2 percent of our 316 million citizens were to die in a modern military engagement, it would equal 6.32 million American lives. At 2.5 percent, it would equal 7.9 million lives.
If you take the approximately 700,000 deaths of the Civil War, and divide by the number of days in the four-year engagement period (1,460), it becomes clear that the Civil War claimed hundreds of American lives per day. Two-thirds of the deaths in the Civil War, however, were not attributed to battle, but to disease exacerbated by harsh living conditions and primitive medical treatment options.