Nathaniel Lyon was born on July 14, 1818, in Ashford, Connecticut; he graduated from West Point in 1841. His military service included fighting the Seminoles in Florida and several battles in the Mexican-American War. Promoted to captain in 1851, Lyon’s immediate pre-Civil War career consisted mostly of garrison duty in California and Kansas. During the seven years he served in Kansas, he developed a strong anti-slavery stance; by 1860, he was violating orders to support the free-state movement in Kansas.

In January 1861, he was ordered to reinforce the U.S. arsenal in St. Louis, Missouri. The arsenal was home to approximately 36,000 muskets, and was the largest arsenal west of the Mississippi River. Finding the defenses inadequate, Lyon and U.S. Congressman Frank Blair raised their own volunteer regiments. Within a few weeks, thousands of men, mostly Germans, joined Lyon’s ranks.

In May 1861, Governor Jackson ordered a portion of the state militia to St. Louis for training. Fearing that pro-Southern elements would attack the arsenal, Lyon forced the militia’s surrender at Camp Jackson without a struggle. While the militiamen were being marched to the arsenal, however, an angry mob swarmed in the streets of St. Louis. As tensions rose the nervous German soldiers fired into the crowd, killing 28 civilians.

A month later, Nathaniel Lyon and Francis Blair, Jr., met Governor Jackson and Sterling Price to settle tensions between the factions. After a lengthy, fruitless meeting, Lyon refused to compromise and ended the meeting by declaring “This means war!”

Lyon organized his men and marched to Jefferson City, occupying the city on June 15, and routed Jackson’s Missouri State Guard at Boonville two days later. Lyon continued to follow Jackson’s retreating forces southward, and on August 10 he attacked the Missouri State Guard and their Confederate allies at Wilson’s Creek. Although outnumbered two to one, his army fought well. Lyon was killed, and the Union army was forced to retreat. Although a defeat, the battle served as a powerful incentive to the Lincoln administration to devote more Federal military resources to Missouri. General Nathaniel Lyon became the first Union general killed in the Civil War.