1860 presidential election,
Republicans, led by
Abraham Lincoln, supported banning slavery in all the
U.S. territories at the time, something which the Southern states viewed as a violation of their constitutional rights and as being part of a plan to eventually abolish slavery. The three pro-Union candidates together received an overwhelming 82% majority of the votes cast nationally: Republican Lincoln's votes centered in the north,
Stephen A. Douglas' votes were distributed nationally and
John Bell's votes centered in Tennessee, Kentucky, and Virginia. The Republican Party, dominant in the North, secured a
plurality of the popular votes and a majority of the electoral votes nationally, so Lincoln was constitutionally elected the first Republican president.
his inauguration, seven slave states with
cotton-based economies formed the Confederacy. The first six to declare secession had the highest proportions of slaves in their populations, a total of 49 percent.
 The first seven with state legislatures to resolve for secession included split majorities for unionists Douglas and Bell in Georgia with 51% and Louisiana with 55%. Alabama had voted 46% for those unionists, Mississippi with 40%, Florida with 38%, Texas with 25%, and South Carolina cast Electoral College votes without a popular vote for president.
 Of these, only Texas held a referendum on secession.
Eight remaining slave states continued to reject calls for secession. Outgoing Democratic President
James Buchanan and the incoming Republicans rejected secession as illegal.
Lincoln's March 4, 1861, inaugural address declared that his administration would not initiate a
civil war. Speaking directly to the "Southern States," he reaffirmed, "I have no purpose, directly or indirectly to interfere with the institution of slavery in the United States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so."
 After Confederate forces seized numerous federal forts within territory claimed by the Confederacy, efforts at compromise failed and both sides prepared for war. The Confederates assumed that
European countries were so dependent on "
King Cotton" that they would intervene, but none did, and none recognized the new Confederate States of America.
Hostilities began on April 12, 1861, when Confederate forces
Fort Sumter. While in the
Western Theater the Union made significant permanent gains, in the
Eastern Theater, the 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.
 To the west, 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 battles raged around the
Siege of Petersburg. Lee's escape attempt ended with his
surrender at Appomattox Court House, on April 9, 1865. While the military war was coming to an end, the political reintegration of the nation was to take another 12 years of the
The American Civil War was one of the earliest true
industrial wars. Railroads, the telegraph, steamships, and mass-produced weapons were employed extensively. The mobilization of civilian factories, mines, shipyards, banks, transportation and food supplies all foreshadowed the impact of industrialization in
World War I. It remains the deadliest war in
American history. From 1861 to 1865, it has been traditionally estimated that about 620,000 died but recent scholarship argues that 750,000 soldiers died,
 along with an undetermined number of
[N 1] By one estimate, the war claimed the lives of 10 percent of all Northern males 20–45 years old, and 30 percent of all Southern white males aged 18–40.