The Rim Worlds Republic and the Marian Hegemony are not perfect comparisons. They existed during different eras, with differing levels of technology, and a different political climate. But I’m going to try and compare apples for apples.
In the Republic’s first 116 years, they grew from 1 world to 23. At least 16 of those were acquired not through colonisation, but by other means. The remaining 6 may have been acquired through similar means, or may be the result of colonising efforts.
In the Hegemony’s first 116 years, they grew from 1 world to 9. All 8 were colonised. In the 94 years since (up to 3130), they have colonised an additional 5, and acquired 15, although they later lost six of those acquisitions.
During the Republic’s 532+ years, 158 of those were known as the Age of War. There was a mass exodus for the periphery. People were colonising it to escape war. This presented them with plenty of targets to annex. There was also a greater level of technology, making colonisation easier. A further 183 years were spent as members of the Star League, much of which was peaceful. The Marian Hegemony was born during the Succession Wars, and was ravaged by the Jihad. They haven’t enjoyed the advantages of time, technology, or stability that the Republic had, yet their goal is much the same. And up until the Jihad, they were well on their way to mirroring the Republic’s growth.
For comparison’s sake, I’ve included a to scale map of both. This was a quick and dirty thing, so the quality isn’t great, but the black areas are the core, that area controlled in their first 116 years, and the rest shows their greatest extent.
