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"battles among fellow citizens or within a community," from civil in a sense of "occurring among fellow citizens" attested from late 14c. in batayle ciuile "civil battle," etc. The exact phrase civil war is attested from late 15c. (the Latin phrase was bella civicus).
Early use typically was in reference to ancient Rome. Later, in England, to the struggle between Parliament and Charles I (1641-1651); in U.S., to the War of Secession (1861-1865), an application often decried as wholly inaccurate but in use (among other names) in the North during the war and boosted by the use of the term in the popular "Battles and Leaders of the Civil War" series published 1884-87 in "Century Magazine."
"The war between the States," which a good many Southerners prefer, is both bookish and inexact. "Civil war" is an utter misnomer. It was used and is still used by courteous people, the same people who are careful to say "Federal" and "Confederate." "War of the rebellion," which begs the very question at issue, has become the official designation of the struggle, but has found no acceptance with the vanquished. To this day no Southerner uses it except by way of quotation .... "The war of secession" is still used a good deal in foreign books, but it has no popular hold. "The war," without any further qualification, served the turn of Thucydides and Aristophanes for the Peloponnesian war. It will serve ours, let it be hoped, for some time to come. [Basil L. Gildersleeve, "The Creed of the Old South," 1915]
The war fought in the United States between northern (Union) and southern (Confederate) states from 1861 to 1865, in which the Confederacy sought to establish itself as a separate nation. The Civil War is also known as the War for Southern Independence and as the War between the States. The war grew out of deep-seated differences between the social structure and economy of North and South, most notably over slavery; generations of political maneuvers had been unable to overcome these differences (see Missouri Compromise and Compromise of 1850). The secession of the southern states began in late 1860, after Abraham Lincoln was elected president. The Confederacy was formed in early 1861. The fighting began with the Confederate attack on Fort Sumter. Most of the battles took place in the South, but one extremely crucial episode, the Battle of Gettysburg, was fought in the North. The war ended with the surrender of General Robert E. Lee to General Ulysses S. Grant at Appomattox Court House. (See Battle of Bull Run, Battle of Chancellorsville, Emancipation Proclamation, and Sherman's march to the sea; also see map, next page.)
Note: The Civil War has been the most serious test yet of the ability of the United States to remain one nation.