The Liberty Arsenal was an United States Army arsenal at Liberty, Missouri in Clay County, Missouri, that was seized by Confederate sympathizers on April 20, 1861, being an early occurrence in a sequence of skirmishes and battles that was to define Missouri in the American Civil War. It has sometimes been called the "Missouri Fort Sumter." It was located generally west of the junction of Missouri Route 291 and old 210 Highway.
After states began seceding from the Union, the Missouri Constitutional Convention of 1861 voted 98-1 on March 21, 1861 to stay in the Union but not to supply men or money to either side. On April 12, 1861, the Civil War officially began with the firing on Fort Sumter.
In the earlier Bleeding Kansas skirmishes and battles, western Missouri around Kansas City, Missouri showed it had strong Southern leanings. On April 20, about 200 men from Clay and Jackson County, Missouri seized the lightly guarded arsenal leaving the St. Louis Arsenal as the only other military arsenal in the entire state.
The Southern sympathizers captured about one thousand muskets, four brass field pieces and a small amount of ammunition. but this was small compared to the 37,000 muskets and rifles believed to have been kept at St. Louis.
The munitions were to be hidden at the home of Henry Lewis Routt near what is now William Jewell College. Routt was eventually captured and tried for treason and sentenced to hang but was pardoned by Lincoln. Instead, a large proportion of the arms were shipped upriver to the charge of St. Joseph mayor M. Jeff Thompson. The arms were distributed to Missouri Militiamen and later to the Missouri State Guard. The four brass field pieces became Capt. Henry Guibor's State Guard battery.