February, 1864, he was put under arrest for falsely representing himself as colonel of the 68th New York Volunteer Infantry Regiment and enriching himself by raising funds from young officers who expected that he could obtain commissions for them in his regiment. He was eventually released and actually appointed colonel of New York's 68th in June, 1864, serving under Brigadier General James B. Steedman in Tennessee and Georgia, he took part in the Battle of Nashville, and toward the end of the war was assigned to the command of the post at Atlanta. Salm-Salm was mustered out of the volunteers on November 30, 1865. On January 13, 1866, President Andrew Johnson nominated him for appointment to the grade of brevet brigadier general, to rank from April 13, 1865 and the U.S. Senate confirmed the appointment on March 12, 1866. After the American Civil War was over, Salm-Salm offered his services to the Habsburg's Emperor Maximilian I of Mexico, and embarked for Mexico in February, 1866. Maximilian was actively promoting American soldiers to migrate to Mexico after the war to improve relations with the country. Salm-Salm was in an unusual position because he had fought for the Union while most of the Americans who moved to Mexico after the Civil War had fought for the Confederacy. By the summer he was appointed colonel and became the Emperor's aide-de-camp and chief of household. He was captured at Querétaro along with the emperor but not before he made a brave charge with his hussar cavalry in an attempt to save Maximilian from the surrounding Mexican Republican army under Benito Juárez. Together with the Emperor and his highest-ranking generals Tomás Mejía Camacho and Miguel Miramón he was sentenced to death by firing squad. Thanks to the tireless efforts of his wife (who had also tried to obtain a pardon for the Emperor Maximilian) he was pardoned by Juárez and released from custody in December 1867. During his captivity, he was promoted to the rank of brigadier general. Soon after, he returned to Europe and re-entered the Prussian Army as major in the 4th Guards Grenadiers regiment. He was killed at Saint-Privat-la-Montagne during the Battle of Gravelotte in the Franco-Prussian War. His faithful wife Agnes who again had joined him, serving as a nurse on the battlefield, had his mortal remains transferred to the family crypt in Anholt Castle, Germany. His memoirs were edited by