You can make applicants who originate from Elysium. The siege is public knowledge and so is the description of the kingdom. You are free to use it in your application.

Elysium is an alpine kingdom that is slightly smaller than Acolyte. It is located further north-east in proximity to the mountains. Elysium primarily uses aircraft to navigate the tricky terrain and are known for aviation, iron ore exports as well as their large concentration of Rhizomites. Acolyte had a neutral relationship with Elysium, however the concentration of Rhizomites troubled Acolyte due to how firmly they were integrated into the kingdom's rule. The way the religious group presented itself was also of concern due its extremist streak which may have motivated Elysium's attack on Acolyte. The specifics of why Elysium attacked are still unclear, but it ruined any chance of a relationship between the two kingdoms.