The Attack on Berhert was an attempt by Yondu Udonta's faction of Ravagers, acting on orders from Ayesha, to kill the Guardians of the Galaxy.
When Stakar Ogord discovered that Yondu Udonta had been involved in child trafficking, thus violating the Ravagers Code, the Yondu Ravager Clan was exiled. They went on Contraxia to have some good time, and after Ogord and Udonta argued about the latter's exile, Udonta and his men were approached by the Sovereign High Priestess Ayesha, who offered to pay the Ravagers a million units for the capture of the Guardians of the Galaxy, who had stolen highly valuable Anulax Batteries from the Sovereign.
Udonta and his Ravagers tracked down the Milano on the planet Berhert, where the Guardians had crashed following the Escape from the Sovereign Fleet. While Star-Lord, Drax the Destroyer and Gamora left Berhert with Ego, Rocket Raccoon, Groot and the captive Nebula remained on the planet.