When the Jixt arrived above Earth’s skies, first contact celebrations with the friendly alien race were cut short when the Jixt warned of the Xir threat.
For months, the Jixt helped us improve our technology and weapons, preparing humanity for the fight against extinction.
The Xir came, and we defeated them. At great cost. But humanity was so eager to befriend the Jixt, the first alien race mankind encountered, that we bought their lie.
The Xir came to save us from the Jixt, and we murdered them.
Humans were massacred. The survivors were scattered throughout the galaxy, living as endangered vagabonds.
Good sf story, but deserves a much longer version. Classic sf theme.