(NOT TO BE CONFUSED WITH THE STARGATES FROM THE STARGATE UNIVERSE)
The Star Gates were used by young space faring races prior to the events of Galactic Civilizations.
As stated in the intro, these devices were used by space faring civilizations to link their worlds together. The immense ancient structures harnessed incredible energy to fold space and send starships across great distances. However, the Star Gates had their limits, for they could only send ships between any two of them. The use of the Star Gates had provided peace and security to those who had collected and constructed them, at the cost of the rest of the galaxy being unexplored and uncolonized. Contact was never made with other races capable of interstellar travel, trade was never realized, and the many empires remained in solitude for many, many years.
This era ended with the rise of the youngest race, humanity. The humans, true to their reckless nature, had developed a technology that would change the galaxy forever: HyperDrive. A ship equipped with HyperDrive is capable of traveling great distances on their own, rendering the Star Gates obsolete.