The Civil War that threatened to destroy the united states between 1861 and 1865, profoundly transformed the political, social, and economic life of the nation. It began as a constitutional struggle, became a test of federal authority, and of opposing political wills. But Soon took on broader dimensions. The initial belief that it would be short in duration proved tragically mistaken.

The seceding states fought to achieve independence, and ironically molded the government of their confederacy on the United States constitution. The Lincoln administration with a crusade to preserve the union, but as casualties increased and political pressures mounted the aims of the war included, the destruction of slavery, and the liberation of the slave. Thus as the U.S. army extended its occupation deep into the south, it took on social and economic, as well as military responsibility. In the end, after four years of armed conflict and at the high cost of 618,000 lives, the Union had been preserved.

• 1861: Robert E. Lee resigns his commission in the United States Army. "I
  cannot raise my hand against my birthplace, my home, my children." Lee then goes to
  Richmond, Virginia, is offered command of the military and naval forces of Virginia, and accepts.
  
  Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas join South Carolina in
  seceding from the Union. These seven states form a new southern union, setting up
  a provisional government called the Confederate States of America.
  
  Jefferson Davis of Mississippi is elected President of the Confederacy for a six-year term.
  
  Confederate troops open fire on U.S. Fort Sumter in Charleston, South Carolina, forcing Union troops to evacuate.
  
  President Lincoln calls for a 75,000 man militia to suppress the"insurrection," this move provokes four remaining southern states, Virginia, Arkansas,Tennessee, and North Carolina, to secede and join the Confederacy.
  
  Kansas enters the Union as a free state.
  
  Colorado and Nevada Territories are organized as Congress begins to consolidate federal control over the West, establishing strong local governments loyal to the
  Union across the region.
  
  California declares for the Union when news of the Civil War reaches the far West more than a month after the attack on Fort Sumter.
  
  Texas joins the Confederacy, forcing its legendary Unionist governor, Sam Houston, out of office.
  
  Congress passes the Homestead Act, which allows citizens to settle on up to 160 acres of surveyed but unclaimed public land and receive title to it after making improvements and residing there for five years.
  
  Idaho Territory organized.
  
  The Kansas Jayhawkers, a supposedly pro-Union guerrilla band organized by Charles J. Jennison, begin marauding across the Missouri border. In December, they attack and occupy Independence, Missouri, burning much of the city and killing many citizens.
  
  Crews working to complete a coast-to-coast telegraph line meet at Fort Bridger in Utah Territory. The first transcontinental telegram, transmitted from Sacramento to Washington, carries a message from the state's Chief Justice to President Lincoln. Completion of a transcontinental telegraph line signals the end for the Pony Express.