《明史·列传·卷二百一十五》
孛来等人每年都到朝廷来献贡，也几次入侵掠夺边关，并以向西进攻瓦剌部落为托辞，几次抢劫三个卫所。
孛来等每岁入贡，数寇掠，往来塞下，以西攻瓦剌为辞，又数要劫三卫。
Each year, Bolai and his followers went to the imperial court to pay tribute, and they also raided and plundered the border several times, using the excuse of an offensive against the Oirats to the west, and they robbed the three guards several times.
<s>[INST] Kindly elucidate the central themes in this passage in English: 孛来等每岁入贡，数寇掠，往来塞下，以西攻瓦剌为辞，又数要劫三卫。 [/INST] Each year, Bolai and his followers went to the imperial court to pay tribute, and they also raided and plundered the border several times, using the excuse of an offensive against the Oirats to the west, and they robbed the three guards several times.</s>
Kindly elucidate the central themes in this passage in English: 孛来等每岁入贡，数寇掠，往来塞下，以西攻瓦剌为辞，又数要劫三卫。
user
Each year, Bolai and his followers went to the imperial court to pay tribute, and they also raided and plundered the border several times, using the excuse of an offensive against the Oirats to the west, and they robbed the three guards several times.
assistant