Alex Cazerne served as a military officer in the Free Planets Alliance, rising to flag officer rank. In 788 UC, he commanded the unit where Yang Wen-li served as his subordinate and tasked Yang with investigating the Tuesday Correspondence, letters alleging war hero Bruce Ashbey was murdered during the Second Battle of Tiamat. This investigation resulted in Yang's transfer to an Econia prisoner-of-war camp. Cazerne married Hortense Milbelle, daughter of a former superior, in February 789 UC. They had two daughters, including Charlotte Phyllis Cazerne. Around this time, he arranged for orphan Julian Mintz to become Yang's adopted son and informally planned Julian's eventual marriage to Charlotte. By 796 UC, Cazerne held flag officer rank and helped Yang secure the Rosen Ritter unit for the new 13th Fleet, aiding in the successful capture of Iserlohn Fortress during the Seventh Battle of Iserlohn. Subsequently appointed chief rear staff officer for the Alliance's invasion of Imperial Territory, he faced supply failures caused by Reinhard von Lohengramm's scorched earth tactics and ambushed supply fleets. As chief of logistics, Cazerne accepted blame for the resulting military disaster and was reassigned to a frontier base. Yang later secured his transfer to Iserlohn Fortress as chief administrator. Serving as Iserlohn's chief administrator under Yang in early 797 UC, Cazerne acted as interim fortress commander during the Alliance Civil War while Yang suppressed rebellions. Later that year, he accepted the defection of Imperial High Admiral Joachim Willibald von Merkatz after the Imperial Civil War. In early 798 UC, Cazerne expressed concerns to Yang about Supreme Council Chairman Job Trunicht's growing political influence. When Yang was summoned to Heinessen for a government inquiry in March 798 UC, Cazerne again assumed command of Iserlohn. During the Geiersburg Fortress attack, he initially favored defense before adopting Walter von Schönkopf's aggressive tactics, holding the fortress until Yang's return. Following Emperor Erwin Josef II's kidnapping and the formation of the Galactic Empire Legitimate Government, Cazerne accompanied the Yang Fleet in abandoning Iserlohn. He organized the evacuation of military personnel and civilians, expressing frustration over Dusty Attenborough's plan that destroyed hundreds of transports. He remained with Yang during the guerrilla campaign and was present at the Battle of Vermillion. After the Free Planets Alliance became an Imperial client state, Cazerne stayed in the Alliance Fleet, serving as acting secretary of logistics at joint operations headquarters and participating in planning a resistance movement under Admiral Merkatz. During the Lennenkampf affair in summer 799 UC, he abandoned the Rebelo-led Alliance government after Yang fled imprisonment. Rejecting a promotion offer from Admiral Rockwell, he joined Yang's loyalists. Cazerne assisted the evacuation from Heinessen to Admiral Merkatz's secret base. When El Facil declared independence from the Alliance on 13 August 799 UC, he supported Yang's decision to delay relocating there due to insufficient military strength to defend the planet.