"Map of the rebellion as it was in 1861 and as it is now" depicts the consequences for the Confederacy of the seizure of Memphis in 1862 and the fall of Vicksburg in 1863 (Harper's Weekly, March 19, 1864)
February 17 – American Civil War: The Confederate submarineHunleytorpedoes the USS Housatonic, becoming the first submarine to sink an enemy ship (the sub and her crew of 8 are also lost).
February 25 – American Civil War: The first Northern prisoners arrive at the Confederate prison at Andersonville, Georgia (the 500 prisoners had left Richmond, Virginia, 7 days before).
May – Man and Nature: or, Physical geography as modified by human action by George Perkins Marsh is published. One of the first works to document the effects of human action on the environment and it helped to launch the modern conservation movement.
May 18 – Civil War gold hoax: The New York World and the New York Journal of Commerce publish a fake proclamation that President Abraham Lincoln has issued a draft of 400,000 more soldiers.
May 26 – Montana Territory is organized out of parts of Washington Territory and Dakota Territory, and is signed into law by President Abraham Lincoln.
June 12 – American Civil War – Battle of Cold Harbor: General Ulysses S. Grant pulls his troops from their positions at Cold Harbor, Virginia and moves south.
July 22 – American Civil War – Battle of Atlanta: Outside of Atlanta, Georgia, Confederate General Hood leads an unsuccessful attack on Union troops under General Sherman on Bald Hill.
July 28 – American Civil War – Battle of Ezra Church: Confederate troops led by General Hood make a third unsuccessful attempt to drive Union forces under General Sherman from Atlanta, Georgia.
October 30 – Helena, Montana is founded after four prospectors (the so-called Four Georgians) discover gold at Last Chance Gulch; it is their last and agreed final attempt at weeks of trying to find gold in the northern Rockies.
November 15 – American Civil War – Sherman's March to the Sea begins: Union General Sherman burns Atlanta and starts to move south, causing extensive devastation to crops and mills and living off the land.
November 22 – American Civil War – Sherman's March to the Sea: Confederate General John Bell Hood invades Tennessee in an unsuccessful attempt to draw Union General Sherman from Georgia.
December 4 – American Civil War – Sherman's March to the Sea: At Waynesboro, Georgia, forces under Union General Judson Kilpatrick prevent troops led by Confederate General Joseph Wheeler from interfering with Union General Sherman's campaign of destroying a wide swath of the South on his march to Savannah, Georgia (Union forces suffer more than 3 times the casualties as the Confederates, however).
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