Gunsmoke, Steam, and Blood
The Civil War accelerated technological development in many areas, but its relatively short duration ensured that the resulting social change was far less drastic than it might have been. Thus, while many cities back East or in Europe now have horseless carriages plying their streets and Babbage Calculators counting the money in their banks, horses and war-surplus slide rules are prevalent in the territories out West and in the economically devastated South.
Walkers are the most visible manifestation of modern technology; huge, hulking machines crouching on two or four legs and standing fifteen feet in height, crewed by at least three men (a “teamster”, or driver; a commander/gunner; and a stoker), and bristling with Gatling guns and casemate mounted six- or (in some larger models) 12-pounder cannon. During the War Between the States, they were painted Union Blue, or in some cases, given white and red striping on their upper hulls and blue on their lower hulls, as during the siege and sack of Richmond in 1863. (The few examples captured and fielded by the Confederates were repainted gray or, in at least one instance, to resemble a stylized Confederate Battle Flag.) For the Indian Wars, attempts have been made to camouflage them by painting them a dull green or khaki, but the thick clouds of smoke they belch have made this an empty gesture at best.
A few of the earliest models (Continental Iron Works Model 1861 “General Washington” Walking Ironclads) have been demilitarized and sold to wealthy cattle barons. These machines are open-topped, with a parasol-like sun-shade atop them, and equipped with a winch. However, their very short range (most walkers have only a few hours of endurance with a full bunker of coal, and the Model 1861 has only 45 minutes at 12 MPH) have made them impractical for anything but range wars.
In the East, Pullman Horseless Carriages have become popular status symbols; the company trains and employs freed slaves to drive them for rich clients, and a “Pullman Teamster” can almost always be found unobtrusively near a robber baron at rest.
Out west, Horseless Carriages are rarely seen, and again, the question of endurance limits their utility. The Army has a few larger versions, fitted with steel boilerplate and equipped with a sort of scoop or ram prow on the front, which they use to construct fortifications. Since the Army already relies heavily on coal, the logistical problems are less severe for them.
Charles Babbage’s Calculator has greatly eased the task of financiers, statisticians, and engineers in the North. Without the six calculators purchased from Lovelace’s of London, it’s questionable as to whether or not Ericksson would have been able to design the first Union walkers, or refine them. Without the example smuggled into Richmond in 1862, the South wouldn’t have been able to prolong the war for a further year after their defeat at Fredericksburg.
In New York and Philadelphia, the police forces have recently begun to experiment with forensic phrenology (AKA Fowlerism, after the brothers Orson and Lorenzo, leading American phrenologists), using large Babbage Calculators to store detailed cranial measurements of every suspect arrested.
The telegraph remains the primary method of long-distance communication, though walkers rely heavily on “wig-wag” signal flags and heliographs. Smaller, cheaper Babbage machines have enabled more rapid and less error-prone morse transmissions to be made via telegraph.
America in 1868 is still making the transition from older cap-and-ball firearms (where the bullet, powder, and primer are all separate components, and each must be introduced to the gun manually or by means of a premade paper cartridge) to much more reliable brass-cartridge rimfire weapons. The process has been complicated because Smith and Wesson has locked up the patent for brass-cartridged revolvers, legally preventing other manufacturers from producing them. As a result, a flourishing trade has arisen in aftermarket conversion cylinders, designed to modify older cap-and-ball weapons into brass cartridge firing weapons. (The process primarily involves changing out the cylinder.)
If a man fought on the Union side of the Civil War, he would likely have used a Colt Army Model 1860 or Remington Model 1858 revolver if an officer or a Springfield Model 1861 rifled musket if an enlisted man. Cavalry would have used a pair of Colt Dragoon revolvers slung over the saddle, later superseded by a Henry or Spencer repeating rifle, along with a (rarely-used) saber.
The Confederacy, with more supply problems, had a greater diversity of weapons, but a Confederate officer would likely have carried a Colt Model 1851 .36 caliber revolver, and regular soldiers would have used the Enfield musket which was virtually identical to the Union Springfield. Marksmen would have used the English-made Whitworth rifle. Cavalrymen would have likely used the Colt Dragoon, or in some cases, the combination pistol-and-shotgun LeMat revolver, or even civilian double-barreled 12-gauge shotguns, as well as a slightly different saber . (Wikipedia has a large and useful list of other weapons used during the war.)
Popular civilian weapons of the era
The .22 caliber Smith & Wesson Model 1 and its larger siblings, the .32 caliber Model 2 and five-shot Model 1 1/2 are the only out-of-the box cartridge revolvers produced domestically in America. Despite their limited stopping power, the ability to load them hours or days before they’re needed without any deterioration in their reliability, as well as their ease of reloading, makes them very popular. Foreign weapons like the British Beaumont-Adams and Tranter, and French Mle 1858 pinfire are also popular, particularly among the wealthy.