Abstract The laws and regulations in human history can be revealed by computational models. From 221 before Christ (BC) to 1912 Anno Domini (AD), the unification pattern has dominated the main part of Chinese history for 2132 years. Before the emergence of the first unified empire, the Qin Empire in 221 BC, there existed the Eastern Zhou dynasty (770 BC to 221 BC). This long dynasty has two stages, and here we focus on the first stage. This Spring–Autumn stage was from 770 BC (with 148 states) to 476 BC (with 32 states). The whole country (China) is modelled as a multi‐agent system, which contains multiple local states. They behave autonomously under certain action rules (wars and conflicts), which forms the main reason for the annexations and disappearance of most states. Key factors (power, loyalty, bellicosity and alliance) have been considered in our model settings, and simulation outcomes will be monitored and collected. Eventually, an optimal solution is obtained, which well unveils the internal mechanism and statistical features of real big history. Furthermore, counterfactuals are used to explore the non‐linear effects of the key factors, which deepens the authors’ understanding of civilisation evolutions in human history.