鼎足之势 [- - zhī shì]a situation dominated by three powerful rivals; a (situation of) tripartite confrontation; political authority or government resting on the coalition of three political parties (suggesting an unstable government)：
•¶ 赤壁之战决定了魏、蜀、吴三国鼎足之势。 The Battle of the Red Cliffs determined the triangular balance of power of the three kingdoms, Wei, Shu and Wu.