Carbine
Early history: before the 1900s
The carbine was originally a lighter, shortened weapon developed for the cavalry. Carbines were short enough to be loaded and fired from horseback, but this was rarely done – a moving horse is a very unsteady platform, and once halted, a soldier can load and fire more easily if dismounted, which also makes him a smaller target (Napoleonic-era and earlier cavalry did fight from horseback, but they fought with sabers and large muzzle-loading horse pistols, so called because their large size meant they were most easily carried in a saddle holster, much like the later Colt-Walker revolver). After the Napoleonic Wars, cavalry began fighting dismounted, using the horses only for greater mobility, an early form of what is today known as motorized infantry. By the American Civil War, dismounted cavalry were mostly the rule. The principal advantage of the carbine was that its length made it very portable. Troops could carry full-length muskets comfortably enough on horseback if just riding from A to B (the practice of the original dragoons and other mounted infantry). Cavalry proper (a "Regiment of Horse") had to ride with some agility and engage in sword-wielding melées with opposing cavalry or pursue running infantry, so carrying anything long would be a dangerous encumbrance. A carbine was typically no longer than a sheathed sabre, and like a sheathed sabre was carried arranged to hang clear of the rider's elbows and horse's legs.
Civil War Spencer Carbine
Carbines were usually less accurate and less powerful than the longer muskets (and later rifles) of the infantry, due to a shorter sight plane and lower velocity of bullets fired from the shortened barrel. With the advent of fast-burning smokeless powder, the velocity disadvantages of a shorter barrel became less of an issue (see internal ballistics). Eventually, the use of horse-mounted cavalry would decline. But carbines continued to be issued and used by many who preferred a lighter, more compact weapon even at the cost of reduced long-range accuracy and power, such as artillery troops, who might need to defend themselves from attack but would be hindered by keeping full-sized rifles around; thus, a common title for many short rifles in the late 19th century was artillery carbine.
During the early 19th century, carbines were often developed separately from the infantry rifles and, in many cases, did not even use the same ammunition, which made for supply difficulties. A notable weapon developed towards the end of the American Civil War by the Union was the Spencer carbine, one of the very first breechloading, repeating weapons. It had a spring-powered, removable tube magazine in the buttstock which held seven rounds and could be reloaded by inserting spare tubes. It was intended to give the cavalry a replacement weapon which could be fired from horseback without the need for awkward reloading after each shot (although it saw service mostly with dismounted troopers and infantrymen, as was typical of cavalry weapons during that war). In the late 19th century, it became common for a number of nations to make bolt-action rifles in both full-length and carbine versions. One of the most popular and recognizable carbines were the lever-action Winchester carbines, with several versions available firing revolver cartridges. This made it an ideal choice for cowboys and explorers, as well as other inhabitants of the American West, who could carry a revolver and a carbine, both using the same ammunition.
The above information is from Wikipedia.