Missouri in the American Civil War

In the American Civil War, Missouri was a border state that sent men, armies, generals, and supplies to both opposing sides, had its star on both flags, had separate governments representing each side, and endured a neighbor-against-neighbor intrastate war within the larger national war.

By the end of the Civil War Missouri had supplied nearly 110,000 troops to the Union and at least 30,000 troops for the Confederate Army and additional bands of pro–Confederate guerrillas. There were battles and skirmishes in all areas of the state, from Iowa and the Illinois border in the northeast to the edge of the state in the southeast and southwest on the Arkansas border. Counting minor engagements, actions and skirmishes, Missouri saw over 1,200 distinct fights. Only Virginia and Tennessee exceeded Missouri in the number of clashes within the state's boundaries.

The first major Civil War battle west of the Mississippi River was on August 10, 1861 at Wilson's Creek, Missouri, while the largest battle west of the Mississippi River was the Battle of Westport at Kansas City in 1864.

Missouri was initially settled by Southerners coming up the Mississippi River and Missouri River. Many brought a few slaves. Missouri entered the Union in 1821 as a slave state following the Missouri Compromise of 1820, in which Congress agreed that no other territory north of 36°30' (Missouri's southern border with Arkansas) could enter the Union as a slave state. Maine entered the Union as a free state in the compromise to balance Missouri.

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