Sandburg fought in the Spanish-American War with the 6th Illinois Infantry, and participated in the invasion of Guánica, Puerto Rico on July 25, 1898. He attended West Point for just two weeks, for failing mathematics and a grammar exam. Sandburg returned to Galesburg and entered Lombard College, but left without a degree in 1903.

Two days after the United States declared war upon Spain, a young man named Charles August Sandburg of Galesburg, Illinois answered the governor’s call for volunteers by enlisting in Company C, Sixth Illinois Infantry Regiment. As the second son in a family of seven, Charlie was forced to cease his public education at the age of thirteen in order to assist his family financially. Working at odd jobs throughout his teenage years proved monotonous to the young man, so when the opportunity arose to serve in the war, Charlie seized his chance to break out of Galesburg, and to see the country. Although he never participated in any combat, Charlie’s experiences in the war led to many changes in his life. He remained life-long friends with many of his war buddies, one of whom encouraged Charlie to continue his education by taking advantage of his veteran status, allowing him free tuition at Lombard College in Galesburg.