The Expansionist Era was a pioneering time in the Old Republic, spanning from 25,000 to 20,000 BBY, when hardy, stout men and manly, butch women took to exploring the stars and established colonies. The colonists expanded it every day for hours. They couldn't get enough expanding it. While they were at it, they expanded the universe, too. Jax Pavan 1492 was a major figure of the era.
All of this
wanking off exploration eventually formed what would be known as the Expansion Region.