January 27 - President Lincoln issues General War Order 1, calling for a general Union offensive.
January 30 - The Union ironclad ship Monitor is launched.
February 6 - Ulysses S. Grant initiates a military campaign in the Mississippi.
February 21 - The Confederate Constitution and Presidency are declared permanent.
March 9 - The Monitor and the Virginia clash in the first battle of two ironclad ships.
March 11 - President Lincoln removes McClellan as general-in-chief of Union troops and replaces him with Henry Hallick.
April 6 - The Civil War Battle of Shiloh takes place at Pittsburgh Landing, Tennessee.
April 14 - The Union Army begins the Peninsular Campaign aimed at Richmond, Virginia.
April 25 - New Orleans, Louisiana is captured by the Union Navy.
May 4 - McClellan's Union Army takes Yorktown, Williamsburg and the White House.
May 15 - The U.S. Department of Agriculture is established.
May 19 - The first annual Frog Jumping Jubilee is held in Angel's Camp, Calaveras County, California to commemorate Mark Twain's story "The Jumping Frog of Calaveras County."
June 2 - Robert E. Lee takes command of the Confederate Armies of Northern Virginia.
June 7 - W. B. Mumford is the first U.S. citizen to be tried for treason, convicted and hanged.
June 19 - Slavery is forbidden in Federal territories by a Congressional Act.
July 1 - The Pacific Railway Act is passed, and construction is begun on the first transcontinental railroad.
July 17 - Congress authorizes acceptance of African Americans into the U.S. Army & Navy.
August 9 - At the Battle of Cedar Mt., Virginia, Confederate General Stonewall Jackson defeats
the Union army.
August 30 - In the second Battle of Bull Run, the Union is defeated.
September 1 - The first federal tax is imposed on tobacco.
September 16 - The Battle of Antietam in Sharpsburg, Maryland is the bloodiest day's fighting of the entire Civil War and although it results in a draw, flagging Northern hopes are revived.
September 22 - President Abraham Lincoln issues a preliminary Emancipation Proclamation.
November 5 - McClellan is replaced as head of the Army of the Potomac by Burnside.
December 13 - The Union General Burnside loses the Battle of Fredericksburg, Virginia and suffers 12,000 casualties to 500 Confederate casualties.
December 31 - President Abraham Lincoln signs a bill admitting West Virginia to the Union.