POLITICAL ECONOMY: Professor Weiwen Yin (University of Macau)

Fractured Land, Revisited: Learning, Memory, and Political Fragmentation

Why did China repeatedly unify while Europe remained fragmented? The fractured-land hypothesis attributes the difference to geography: mountains and seas impede conquest, and a large productive core sustains a large state. We revisit a quantitative version of the hypothesis in which wars arrive by a lottery that favors productive land, and replace it with decisions. Each border cell decides whether to attack a neighbor and learns from the outcome. Experience is stored either in a Q-learning table that treats every situation separately or in a network, wired after the memory center of the fruit fly, that transfers lessons across situations. Europe remains divided under both learning rules, as the hypothesis predicts. China does not unify on geography alone: on the same map it unifies when experience is shared and usually stays divided when it is not. In Japan, the same geographic change moves the two learning rules in opposite directions as well.