Short answers, pulled from the story.
Christopher Spencer invented the Spencer repeating rifle in 1860. He designed the lever-action mechanism and went on to demonstrate the weapon personally for President Abraham Lincoln shortly after the Battle of Gettysburg in 1863.
Over 200,000 Spencer rifles and carbines were manufactured between 1860 and 1869 by the Spencer Repeating Rifle Co. and the Burnside Rifle Co. in the United States.
The Department of War's Ordnance Department feared soldiers would waste ammunition and that the Army's logistics chain could not supply enough rounds for a weapon capable of firing several times faster than a muzzle-loader. The Spencer also cost several times more per unit than a Springfield Model 1861 rifled musket.
The Spencer produced a sustainable rate of fire in excess of 20 rounds per minute. Standard muzzle-loading rifles of the period fired at 2-3 rounds per minute.
Shortly after the July 1863 Battle of Gettysburg, Spencer secured an audience with Lincoln and demonstrated the rifle on the White House lawn. Lincoln ordered General James Wolfe Ripley to adopt it for production. Ripley disobeyed and was removed as head of the Ordnance Department later that year.
Argentina purchased 500 carbines between 1865 and 1869 for its cavalry and navy. Many surplus carbines were sold to France for use in the Franco-Prussian War in 1870. Chilean cavalry adopted Spencer rifles in the summer of 1870-1871, and Falisse and Trapmann in Liege produced just under 1,000 carbines for Brazil between 1873 and 1874.