The stamp was issued to fulfill a need for a reduced rate, 2-Cent denomination for newspaper, magazine, and local deliveries; and was often used to "make up" higher rates, or split in half to make up lower ones (a 1-Cent stamp) due to shortages at the local post office.
During the Civil War, the "Black Jack" was supposed to have been favored by both North and South, but as soon as the South got wind of the North making a stamp depicting one of their own heroes, they printed a 2-Cent stamp of their own in reaction.
After the War was over, poverty forced people to wash off the cancels from the stamps and attempt to use them over again, such that the Government decided to put an antitheft device onto the stamps known as a grill. This grill, which consisted of various rows of tiny indentations into the stamps, was supposed to make it impossible to wash off the cancellations without being detected; but thieves usually got around this by bisecting the stamp, and then reusing that portion that didn't have a cancel on it.
Today, collectors cherish stamps that have fancy or colored cancels on them, or especially if they are still on their original covers. Covers that have multiple stamps on them, or are part of a multiple rate with several stamps of all denominations, are the most desirable.
Unlike foreign stamps, especially German stamps, United States bisected stamps are usually only valuable if they remain on their respective covers. Once taken off, they are worthless.
The most famous bisected Black Jack stamps are known as "stage cents" bi-sects, and occurred after the Civil War when Southerners would cut 2-Cent stamps vertically in half between the "O" and "S" of the word "POSTAGE" at the top of the stamp. The result was that the wording that was left on the right-hand portion of the stamp would say "STAGE CENTS" – subtly referring to the assassination of President Abraham Lincoln by the actor John Wilkes Booth. If anyone had any questions, the creator of the bi-sect would simply tell him that he was only intending to use the left-half portion of the stamp, which read "U.S.PO TWO"; and footnoted it saying that he was truly sympathetic towards the causes of the poor and The Union.