The American Civil War, widely known as simply the Civil War, was fought from 1861 to 1865 to determine the survival of the United States of America or the independence of the Confederate States of America. Among the 34 states in January 1861, seven Southern states declared their secession from the U.S. and formed the Confederate States of America. The Confederacy, or the South, grew to include eleven states.  It claimed two more border states (Kentucky and Missouri), the Indian Territory, and the southern portions of the Union’s western territories of Arizona and New Mexico, which was organized and incorporated into the Confederacy as Confederate Arizona. The Confederacy was never diplomatically recognized by the United States government, nor was it recognized by any foreign country. They produced their “Articles of Secession” declaring their break from the Union.  Four states went further.  Texas, Mississippi, Georgia and South Carolina all issued additional documents, usually referred to as the “Declarations of Causes” which explained their decision to leave the Union. All states strongly defended their states’ rights.  Other grievances included taxation, economic exploitation, such as tariffs, the role of the military and slavery.  The states that remained loyal, including the Border States, were known as the Union or the North.

The North and South quickly raised volunteer and conscription armies that fought mostly in the South over four years. During this time, many innovations in warfare occurred, including the development, and use of iron-clad ships, ultimately changing naval strategy around the world.

Hostilities began on April 12, 1861, when Confederate forces fired upon Fort Sumter.  The First Battle of Bull Run also known as Battle of First Manassas was fought on July 21, 1861 in Prince William County, Virginia, just north of the city of Manassas and about 25 miles west-southwest of Washington, D.C. It was the first major battle of the Civil War and a Confederate victory as the Union‘s forces were slow in positioning themselves which allowed Confederate reinforcements time to arrive by rail.  While in the Western Theater the Union made significant permanent gains, in the Eastern Theater, battle was inconclusive in 1861–62. The autumn 1862 Confederate campaigns into Maryland and Kentucky failed, dissuading British intervention. Lincoln issued the Emancipation Proclamation, which made ending slavery a war goal.

By summer 1862 the Union destroyed the Confederate river navy, then much of their western armies and seized New Orleans. The 1863 Union siege of Vicksburg split the Confederacy in two at the Mississippi River. In 1863, Robert E. Lee‘s Confederate incursion north ended at the Battle of Gettysburg. Western successes led to Ulysses S. Grant‘s command of all Union armies in 1864. Inflicting an ever-tightening naval blockade of Confederate ports, the Union marshaled the resources and manpower to attack the Confederacy from all directions, leading to the fall of Atlanta to William T. Sherman and his march to the sea. The last significant engagement was the Battle of Appomattox and ended with General Robert E. Lee’s surrender to General Ulysses Grant at the McLean House, in the village of Appomattox Court House, on April 9, 1865.

After four years of intense combat that left more than 750,000 Americans, (including civilians) Union and Confederate, dead and destroyed much of the South’s infrastructure, the Confederacy collapsed, grievances were addressed and slavery was abolished in the entire country. Then began the Reconstruction Era (1863–1877) and the process of restoring national unity, strengthening the national government, and guaranteeing civil rights to the freed slaves.  The political reintegration of the nation during the Reconstruction Era would take another 12 years.