Peace with Great Britain and the end of the Indian peril brought change to the Kentucky Militia. Ever since Kentucky became a state, it had, like other states, maintained an enrolled militia system. This required nearly every man to sign up for militia service, provide himself with a weapon, and attend periodic training sessions called musters. With no serious enemies in view, most Kentuckians paid little attention to the enrolled militia. Musters, when held at all became social gathering that featured more drinking that drilling. Laws, which required participation in the militia, were not enforced.
A new type of militia — the volunteer militia — became popular. Men interested in part-time military service formed the volunteer militia companies. Often the social elite in their communities, volunteer militiamen purchased stylish, expensive uniforms. They competed with other companies for snappy performance of the complicated maneuvers of the 19th-century tactics. Unable to rely upon the enrolled militia, Kentucky and other states called upon volunteers to fill the regiments of soldiers required of the states by the federal government during crises.
The most serious crisis during this period concerned Texas. Many Americans, including Kentuckians, had moved west and settled in Texas, then a part of Mexico, by the 1830s. In 1836 Texas fought a revolution to obtain its independence from Mexico. Kentuckians went west to help the Texans, and many of them met their deaths at the Alamo and Goliad massacres. Kentucky volunteers provided vital manpower for the final Texas victory at the Battle of San Jacinto. For ten years the Republic of Texas was a separate nation.
In 1846 after Texas was granted statehood, an act which was intolerable to Mexico, war broke out between the two countries. Kentucky provided three infantry regiments and a mounted regiment for this war. The Louisville Legion, a volunteer militia battalion, provided most of the men for the First Kentucky Infantry, while men for the Second and Third Regiments came from Lexington, the mountains of eastern Kentucky, and other parts of the state. Many of the Kentuckians fought at the Battle of Buena Vista, where General Zachary Taylor won a decisive victory over the Mexicans under General Santa Anna. A few Kentucky volunteers fought under General Winfield Scott in the campaign which led to the conquest of Mexico City.
The Third Kentucky Regiment was part o the occupation force that garrisoned the Mexican capital until a peace treaty was signed. Many Kentuckians who fought in this war would put this military experience to good use in a much bigger war a dozen years later. Interest in the militia diminished again after the Mexican War. A major reform of the Kentucky Militia system was attempted in 1860. General Simon Bolivar Buckner tried to establish a statewide organization taking in the many volunteer militia companies. He envisioned Kentucky as having it's own miniature army with distinctive uniforms, high quality weapons, and thorough training. He called this force the Kentucky State Guard. Only the name lasted, however. The coming of the Civil War put an end to Buckner's plans.
In 1861 tension between the northern and southern sections of the United States tore the country apart. Kentuckians found themselves caught between the warring factions. Most Kentuckians supported the Union, but they believed slavery was essential to their prosperous economy. It took the state some months to decide which way to go in the war. Governor Beriah Magoffin declared Kentucky neutral and ordered General Buckner's Kentucky State Guard to repel the soldiers of either the Union or the Confederacy should they enter Kentucky.
Individual Kentuckians made their own decision. The State Guard proved to be largely loyal to the Confederacy. Entire companies march away to recruiting camps in Tennessee. Some of the Union men formed Home Guard companies. The federal government shipped weapons, called "Lincoln Guns," into Kentucky to arm them. Others enlisted in volunteer regiments, the first at recruiting camps north of the Ohio River and later at camps within Kentucky.
By the end of 1861, Kentucky State government had declared itself loyal to the Union and federal forces occupied the northern half of the state. The Kentucky State Guard had disintegrated, but Confederate troops were in place at strategic locations across southern Kentucky. Eventually about 100,000 Kentuckians served in the Union Army. They made up 52 infantry regiments, 15 cavalry regiments, and 6 artillery batteries. Black Kentuckians, attracted by a promise of freedom from slavery in exchange for enlisting in the army, filled several Union Regiments.
Kentucky’s Union regiments fought all across the war’s western theater. They saw heavy combat in their home state and in Tennessee, Mississippi, and Georgia. About 40,000 Kentuckians fought in the Confederate Army. Many of them were in the First Kentucky Orphan Brigade, one of the most famous units on either side during the Civil War. Other Kentuckians made reputations as dashing cavalrymen serving under John Hunt Morgan and Nathan Bedford Forrest. Their raids into Kentucky destroyed important Union supplies and facilities and kept thousands of Union soldiers busy guarding railroads, bridges, and warehouses.
The Confederates lost Kentucky during the 1862 campaign. After the Battle of Perryville in October, fighting involving the major armies moved south of Kentucky’s borders. But there was no peace in Kentucky. Guerillas terrorized the state. Some of these bands of raiders supported the Union or the Confederacy, but many were simply lawless bandits who took advantage of wartime chaos to rob or murder their neighbors. Union authorities in Kentucky took drastic measures to control the guerillas measures so harsh that many Kentuckians who had supported the Union turned against federal authority by the end of the war. The Kentucky State Guard was reorganized as a pro-Union force with battalions across the state to hunt down guerillas.