Prior to the arrival of the Imperians, the Mariner races in each star system traded and mingled to various extents. Only Illyricans and Cappadocians had discovered posterns and ventured into them. Once the Imperians arrived and began their takeover, the Mariner races were absorbed and assimilated. Some, like the Aquitani and Iceni, resisted more than others.
Following the Imperians came the Renanim. They originated on the same distant, dying planet, but had stayed to attempt to save the planet. When it became clear the planet was unable to be saved, they followed breadcrumbs left by the Imperians into the Europa System.