Union Cavalry:

In 1859 the United States Army and many State Militias supported small regiments of Cavalry to be integral to their Militias arms of defense. 

Cavalry units tended to be mustered together less often at first due mostly to the expense of arming, equipping soldiers and maintaining horses.   Exceptions to the rule in the  Southern and Western regions of the United States, were largely due to the number of privately owned horses at hand used everyday by the citizens and settlers of those regions.  At the outset of the war there many state cavalry units mustered for Lincolns call to arms.  The War Dept. decided that unless these units were fully equipped for that role, the expense of horses and equipments forced these units to be organized for uses as Infantry or Artillery and others between.

4th Massachusetts Cavalry:

The 4th Massachusetts was organized and equipped as most Union Cavalry regiments were which served the for the United States. 

The third battalion companies I,K,L & M, were Veterans of the South Carolina and Florida Campaigns and were originally part of the 1st Massachusetts Cavalry Regiment. They were issued uniforms, arms, and equipments typical of regular Union Army issue.  Mounted trousers, Sack Coats, Mounted Service jackets with yellow trim, brogans or boots, Forage caps and kepis, shirts, socks etc... 

Initially the men were first armed and issued only sabres they received firearms as they became available.  Each trooper was eventually issued in addition to a saber, one Colt pistol, and a Sharps carbine.  

The Breech loading Sharps carbine was considered before the war to be one of the most advanced weapons of its day.  Because it was loaded without having to use a ramrod the time between firing shots was greatly increased.  This innovation combined with rimfire metal cartridge ammunition, would eventually evolve to multiple cartridge magazine fed rifles and carbines. 

 By 1864 the 4th Massachusetts Cavalry would be one of the lucky regiments issued Spencer repeating carbines.  The Spencer Repeating Carbine gave the Union Cavalry a substantial advantage against their southern counterparts.  Yet even though it was vastly superior, few were issued compared to the Sharps Carbine due to the oversight with its cost and available supply.

Confederate Cavalry:

Confederate Cavalry held the advantage early in the war having skilled horsemen, shooters, and fencers.  Living in vast rural areas between towns horses were a necessity that larger industrial communities in the north didn't seem to have as much need for.  The Industrial North factories provided housing, churches, schools and company stores and grocers within walking distance.  Where as the Southern Agrarian Culture of plantations and farms were miles apart between towns. 

The skills for fighting on horseback, actively hunting and riding, tended to give Southerners and Westerners an advantage even before the war and many of the Cavalry Officers who served the Confederacy had also received formal military training and served in the United States Army on the Frontier. 

As hostilities began many Northern leaders made allegations of Southern leaders as having directly engineered the promotion of their own kith and kin to control the military, let alone the country.  These allegations would add fuel to the fire and many Southern Unionist would be viewed with speculation for whom their loyalties were with.  Though a Majority of Officers in United States Cavalry were of Southern birth or affiliation there is little documentation to prove a conspiracy for their elevation in the U.S. military.  As secession took hold most southern soldiers would resign their commissions with the United States to return home and in defense their native states with Southern Confederacy.