In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What tribe did Borte join unwillingly?, Context: As previously arranged by his father, Temüjin married Börte of the Onggirat tribe when he was around 16 in order to cement alliances between their respective tribes. Soon after Börte's marriage to Temüjin, she was kidnapped by the Merkits and reportedly given away as a wife. Temüjin rescued her with the help of his friend and future rival, Jamukha, and his protector, Toghrul Khan of the Keraite tribe. She gave birth to a son, Jochi (1185–1226), nine months later, clouding the issue of his parentage. Despite speculation over Jochi, Börte would be Temüjin's only empress, though he did follow tradition by taking several morganatic wives.
Merkits