Left silk-radical 纟 (contracted form of 糸) - the indexing radical. Anchors 绑 in the family of cord-and-binding verbs: 系 (tie), 缠 (wind), 缚 (bind). The thread is what does the tying.
Right 邦 supplies the sound (bāng → bǎng, just a tone shift). 邦 originally meant a fortified territory - semantically distant, so it functions purely as a phonetic loan. Same phonetic family: 帮 bāng (help), 梆 bāng (clapper).
