Wei, Shu, and Wu formed a tripartite balance — known in history as the Three Kingdoms period.
Tips
history
From 《史记·淮阴侯列传》: Kuai Tong advised Han Xin that 三分天下，鼎足而居，其势莫敢先动 — dividing the realm three ways, like the legs of a ding tripod, would create a stable deadlock. The image became fixed as 三足鼎立.
culture
The canonical example is the Three Kingdoms period (220-280 CE), where Wei, Shu, and Wu locked each other in stalemate — familiar to any student via 《三国演义》. Modern usage: any three-way market or political rivalry.
