The Expansionist era officially ended the New Empire era in 100 NE. It is so named for the actions of Empress Domina Walker, granddaughter of the first Emperor, Josh Walker. She kicked off the process of annexing the region of the galaxy formerly known as the Unknown Regions, which had been explored and mapped less than a century before. This era saw the size of the Galactic Empire double.
The Expansionist era lasted from 100 NE to 307 NE