This page gives a summary of Noxus and its history in Factions. More information is available on the Noxus page in the League of Legends wiki, which can be found here.
Noxian society values strength above all. It is a fiercely (often bloodily) meritocratic civilization that embraces conflict and competition. While it is similar to its rival Demacia in that it is ruled by a military dictatorship, the Noxian High Command holds its power not through ideology or the loyalty of its subjects but through a network of power relationships: generally speaking, each person in the Noxian hierarchy holds their position because those below them believe their own interests lie in supporting them, or are simply terrified of them. Noxians are among the most fearsome warriors in Valoran. The League was formed because Noxus assented to its formation, perhaps believing that it could outmaneuver Demacia in the Institute, or perhaps that Noxian warriors would prove superior to Demacians on the Fields, where they could not hide behind legions of indoctrinated peasants.
Jericho Swain took command of Noxus and became its Grand General after unseating (and then beheading) Boram Darkwill. Swain is an outsider who has embraced the “New Noxus” movement, pursuing victory at any cost and making extensive use of Zaunite biochemical weaponry and military industrialization. He is opposed by the Reformists, who believe that this New Noxus too readily sacrifices honor and true individual strength in its all-consuming drive to destroy its enemies.
The Noxian military was all but destroyed in the Void War and the subsequent battle for Shon-Xan. Many Reformists saw this as their chance, and rose up in an insurrection—only to discover that Swain had secretly been gathering his forces, which he deployed (together with Zaunite reinforcements) to massacre the Reformist rebels. Swain’s powerbase now appears to be quite secure.
Noxian magic is quite varied. Most of it would be considered “dark” under conventional arcane taxonomies, and scholars have even identified a rudimentary aspect of necromancy in the oldest Noxian arcane lineages. While Demacian magic is fairly homogeneous, fueled by cosmic power that overwhelms the individual and transforms them into a mere conduit for celestial energy, Noxian magic is tightly linked to the individual wielder, and thus expresses itself in a variety of forms. Shadow magic that allows the caster to conceal their presence, or move seamlessly from point to point via teleportation, is something of a specialty, as is the enchanting of blacksteel weaponry with bloodrunes to create fearsome blades capable of cleaving through Demacian plate. Recently, Noxus has also begun to adopt Zaunite techmaturgic “strategic” munitions, infamously deployed during both invasions of Ionia.
In Mirrorwater Noxus emerged second out of the five factions involved.
During Ceruleana Noxus was eliminated from the dispute partway through.
Noxus did not participate in the Discord dispute, but it was attacked by the Discord near the conflict's end. They survived the attack and drove the forces of the Void and Shadow Isles back, but suffered severe losses.
Noxus was defeated in the dispute for Shon-Xan by Ionia. Their navy and army took many losses when Demacia and Ceruleana prevented their landing on the island. Noxus did managed to hold onto a small piece of land in Shon-Xan, though it was inhospitable due to chemical bombings they called in.
In arc VII, Lines in the Sand, Noxus emerged victorious over the three factions competing.