The city of St. Louis was a strategic location during the American Civil War, holding significant value for both Union and Confederate forces. As the largest city in the fiercely divided border state of Missouri and the most important economic hub on the upper Mississippi River, St. Louis was a major launching point and supply depot for campaigns in the Western and Trans-Mississippi Theaters. Background Located at the junction of the Missouri, Illinois and Mississippi Rivers, St. Louis was a major port and commercial center with a rapidly growing industrial base. The population reached 160,000 in 1860 and consisted mostly of recent immigrants, especially Catholic German Americans and Irish Americans. Early Union volunteer regiments in St. Louis were composed largely of the dominant German immigrants. The only major city west of the Mississippi River in the geographic center of the country, St. Louis had also emerged as the gateway to the new American frontier. It had long served as the starting point for voyages of exploration and emigration into the unsettled West and as the westernmost terminus of many early efforts to construct transcontinental lines of transportation and communication. Camp Jackson Affair In March 1861, Captain Nathaniel Lyon arrived in St. Louis in command of Company B of the U.S. 2nd Infantry Regiment. At the time, the state of Missouri was relatively neutral in the dispute between North and South, but newly elected Missouri Governor Claiborne Fox Jackson was a strong Southern sympathizer. Lyon was concerned that Jackson meant to seize the federal arsenal in St. Louis if the state seceded and that the Union had insufficient defensive forces to prevent its capture. He attempted to strengthen the defenses, but came into opposition with his superiors, including Brigadier General William S. Harney of the Department of the West. Lyon employed his friendship with Francis P. Blair Jr. to have himself named commander of the arsenal. When the Civil War broke out and President Abraham Lincoln called for troops to put down the Confederacy, Missouri was asked to supply four regiments. Governor Jackson refused the request and ordered the Missouri militia to muster outside St. Louis under the stated purpose of training for home defense. Lyon allegedly disguised himself as a farm woman to spy on the militia camp and confirmed the presence of artillery stolen from a federal arsenal. Lyon himself had been extensively involved in the St. Louis Wide