One of the early battles during the American Civil War, and a second major Union defeat within a few weeks of the disaster at First Bull Run. Missouri was one of the most divided of all the states, with a pro-Southern governor but enough pro-Union sentiment to have elected an anti-secession Convention that voted 89-1 to stay in the Union.
This did not stop Governor Claiborne Jackson from continuing to work towards secession. One of his main targets was the large Federal arsenal at St. Louis. With artillery provided by Jefferson Davis, Jackson hoped to seize the arsenal and use it to arm his pro-southern militia.
This plan was disrupted by the commander of the armoury, Captain Nathaniel Lyon. He was unwilling to let the secessionists seize the weapons in his care, and in early May arranged to hand them over to the Illinois militia, safely pro-Union. After that he had broken up the threatening militia camp. Jackson had responded by appointing Stirling Price to raise a pro-Confederate army. A brief truce between Price and the Federal commander, William S. Harney, came to an end soon after Harney was replaced by Lyon, now promoted to brigadier-general. On 11 June a meeting between Lyon and Frank Blair on the Union side and Jackson and Price on the Confederate ended after it became clear that neither side was willing to make the sort of concessions that wound have been needed to maintain the truce.
Lyon now launched a campaign that forced Price to retreat into the south west corner of Missouri. Although Price had managed to raise 8,000 men, against Lyon's 5,500, the Confederate forces were badly armed (perhaps as many of 3,000 had no arms at all!). However, Price was now reinforced by 5,000 men under General Ben McCulloch, giving him a massive advantage over Lyon.
Rather than pull back towards St. Louis, Lyon decided to launch a surprise attack on the Confederate camp at Wilson's Creek. He sent a force of 1,200 men on a flanking march that would bring it out in the Confederate rear, while he attacked them in front with the remaining 4,300.
Lyon's plan started well. The flanking march, under Franz Sigel, succeeded in surprising the rebels. However, at this early point in the war many units wore similar uniforms and this often caused misunderstandings. Here, units on both sides were wearing gray. This resulted in a case of mistaken identity that allowed a Louisiana regiment to get close enough to Sigel’s men to unleash devastating musket fire that broke up Sigel’s attack. This allowed the Confederates to concentrate against Lyon’s frontal assault.
Lyon's men were now outnumbered three to one, 13,000 Confederates again 4,300 Federals. The outnumbered Union men were already running short of ammunition when Lyon was shot and killed. This took the heart out of the Federal attack, and the attack was soon called off. The battered remnants of Lyon's army withdrew, first to Springfield, and then back to Rolla in the centre of the state. Both sided suffered heavy losses at Wilson's Creek - Confederate losses were around 1,200, Union just over 1,300.
The Confederates were too badly battered to pursue the defeated Federal army, having lost 1,200 men. However, they soon recovered, and during September launched an invasion of north Missouri that resulted in the capture of Lexington (18-20 September), one of the largest cities on the Missouri River. However, Price was not able to maintain this position, and was soon forced to retreat back into the same south west corner that he had been in before the victory at Wilson's Creek.