<answer>Tibet</answer> was once a strong power contemporaneous with Tang China (618–907). Until the <answer>Tibet</answer>an Empire's collapse in the 9th century, it was the Tang's major rival in dominating Inner Asia. The Yarlung rulers of <answer>Tibet</answer> also signed various peace treaties with the Tang, culminating in a treaty in 821 that fixed the borders between <answer>Tibet</answer> and China.
Who was the Tangs biggest rival?
Tibet