Cockroaches
A long time ago, humanity was not the domineering and all-conquering race that everyone in the Milky Way and the Red Ocean was familiar with. When humans escaped the confines of their home planet and spread across the stars, they did so with a lot of hope and optimism.
It was too bad that the galactic scene of the Milky Way was already old. Many different alien races had risen up much earlier than humanity and already carved up everything of value.
The situation back then largely resembled the state of the Red Ocean but at a much larger scale.
Many of the more powerful alien races that had come to dominate a significant amount of territory had reached a stalemate against their neighbors and competitors.
This produced a shaky balance of power that occasionally broke from time to time, allowing different civilizations the opportunity to alter the circumstances in their favor.