The Peninsular-Vault War was an armed conflict fought between the forces of the Peninsular Empire and the dwellers of Vault 24 between 2238-2246. It resulted in the defeat of the Vault dwellers and the dismantling of their small empire. It was subsequently incorporated into the Peninsular Empire as the District of Eastern Saginaw.
The Peninsular Empire had conquered most of the western lower Peninsular by the early 2210s. They subsequently case their eyes southwards and advanced slowly but surely, defeating or incorporating many small tribes and settlements into their territory. They did not encounter any major obstacles until reaching the former settlement of Bay City. There they would encounter the heavily armed Vault Dwellers.
Vault 23 had been a control vault set to open after 100 years. When the signal was received the Dwellers spread out to begin settlements on the surface using their GECK devices. They were highly successful and their population boomed. Their leaders became aggressive and soon began attacking surrounding tribals in order to take slaves. By 2215 Vault 23 ruled over much of the eastern Saginaw peninsula, with its core population of ~7000 Vault Dwellers and several 10s of thousands of tribal subjects. This represented a formidable force in the area, and only the relative isolation of the Vault Dwellers prevented their spread. They also lacked enough technology to equip their troops and hoarded it in the Vault for safekeeping.
The Peninsular Republic reached the border with Vault 23 territory in 2214. They demanded the Vault Dwellers submit themselves and become citizens of the Empire or face war. Their emissaries were sent back in jars as glowing ash, having been fed to a fusion reactor.