Memorial Day is an opportunity to recognize not just active or retired members of the U.S. armed services, but also those who came before. Almost half of the 1.25 million Americans who've died fighting for their country were killed in the Civil War, on domestic soil.

It's estimated that at least 618,222 Union and Confederate soldiers died. The casualties were slightly higher on the Northern side. The horror of the carnage was captured by Harvard University President Drew Gilpin Faust in the acclaimed, "The Republic of Suffering: Death and the American Civil War."

The most casualties were suffered at the most historic battle: Gettysburg. Over three sweltering July days in the Pennsylvania countryside, Robert E. Lee's Army of Northern Virginia had 28,000 deaths, while 23,000 soldiers in the Union's Army of the Potomac were killed. The southern forces had to retreat, paving the way for the Union's victory in the war.

The next deadliest conflict for America was World War II, with more than 400,000 casualties. This was almost four times the number of American losses in World War I. Yet it paled compared with the estimated 8.7 million military deaths suffered by the Soviet Union, or the 5.5 million Germans, 3 to 4 million Chinese or more than 2.1 million Japanese.

The Congressional Research Service puts Vietnam War casualties at 58,330, and 36,574 Americans died in the Korean War. There have been about 6,700 Americans killed in Iraq and Afghanistan.

(Albert R. Hunt is a Bloomberg View columnist. E-mail him at ahunt1@bloomberg.net or follow him on Twitter.)

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