Liscum joined the 1st Vermont Infantry in May 1861 to serve in the Union Army during the American Civil War and by June was on the front lines participating in the Battle of Big Bethel.

[4][1] Following nine months of recovery from his wounds, Liscum was stationed in the Philippines during the Philippine–American War; he was first placed in charge of a brigade in the Eighth Army Corps and later made commander of the 9th U.S.

[1] As the need for foreign troops in China became apparent during the Boxer Rebellion, Liscum and his 1,350 men were dispatched to the Taku Forts, arriving on July 9, 1900, only four days before the assault on Tianjin was to begin.

[1] As Liscum and Robert Leamy Meade were among the last to arrive at the Eight-Nation Alliance fort, they were unable to participate in the planning of the attack and were instead subject to the will of British Royal Engineers General Arthur Dorward.

However, due to poor planning and miscommunication, Liscum led his men to the right across open ground in plain view of Chinese snipers equipped with modern rifles.