Complex sentence: The protector general, in the stead of the king of Yanqi, thereafter submitted tributes to Tang--but when his emissary arrived in Chang'an, Emperor Taizong rebuked him and stated, I attacked Yanqi.
Split into simpler sentences: The protector general, in the stead of the king of Yanqi, thereafter submitted tributes to Tang. But when his emissary arrived in Chang'an, Emperor Taizong rebuked him and stated, I attacked Yanqi.