The technological bases of the colonies that were founded after the other ships had crash-landed on Moria and Umoja were always a step behind that of Tarsonis. (The fourth ship was lost with all hands when it had attempted to land.) When the colonies made contact with one another sixty years later, Tarsonis was the most advanced and prosperous among them.
All three colonies had spread to other worlds and developed their own self-supporting economies, and initially Tarsonis pushed for a conglomerated government. Faced with the likely pre-eminence of Tarsonis in such an arrangement, both Moria and Umoja steadfastly refused. The ruling families of Tarsonis responded by expanding their military and colonizing more aggressively, forming the Terran Confederacy and eventually clashing with the Morians in the Guild Wars. Following nearly four years of brutal warfare, the Confederates declared victory after “negotiating” peace with the Kel-Morian Combine. The outcome of these wars secured the Confederacy’s position as the major power in the sector – with Tarsonis as the central hub of its governance and economy. In theory each Confederate planet had its own senators, but in every meaningful way, the Confederacy was ruled from the bustling metropolis of Tarsonis City, the planetary capital of Tarsonis.
Tarsonis was a temperate planet, and the terrans had expanded quickly to establish cities and industry over much of its surface. At the height of the Confederacy’s power, huge quantities of money and materials were shipped in from the colonies daily. The economic boom on the planet dwarfed that of any other terran world in the Koprulu sector, and Tarsonis’s population grew exponentially. The dynastic ruling families of Tarsonis became more avaricious and corrupt as they built their personal fortunes and vied for more power. As the divide between rich and poor became ever wider, discontent and outright insurgency built up across the planets of the Confederacy. The ruling families responded with increasingly violent measures to keep the colonies in line, culminating in the nuclear decimation of Korhal IV when it attempted to secede from Confederate rule.
Outcry at the destruction of Korhal laid the seeds for the final overthrow of the Confederacy. Arcturus Mengsk formed the Sons of Korhal and rose from leading a terrorist organization to heading a full-blown interplanetary rebellion. When the zerg invasion began, the Confederacy was already struggling to survive; as the Swarm descended on Terran space, the Sons of Korhal seized the opportunity to deal the Confederacy a deathblow. Despite bitter fighting, Tarsonis was overrun and utterly devastated by the zerg. It is estimated that upwards of two billion people were killed. Shortly afterward, the zerg abandoned the planet for reasons unknown.
In the aftermath of the zerg invasion, the Sons of Korhal drew together the remnants of the Confederacy to form the Terran Dominion, ruled by Emperor Arcturus Mengsk. Refugees from Tarsonis have been absorbed into other colonies, and the planet itself has not been re-colonized. The Terran Dominion has placed Tarsonis under strict quarantine while the Dominion’s salvage teams sift through the rubble for any Confederate technologies and military secrets that may have survived the assault. Despite all of this, Emperor Mengsk has made a promise to the scattered refugees of this once-vibrant world: Tarsonis shall be restored, and the Dominion shall help guide it toward a brighter future.