The postwar electoral dominance of the Liberal Democratic Party (LDP) was founded on (1) strong incumbency advantage, which insulated its legislators from declining party popularity, and (2) the malapportionment of districts, which overvalued the electoral clout of the party's rural base. The LDP's demise in 2009 was due to the reversal of both factors, each of which was related to electoral reforms in the 1990s. First, I demonstrate that elections are becoming more “nationalized,” due to the growing weight that voters attach to the attractiveness of party leaders. Past performance has become a poorer predictor of incumbent reelection, giving way to large partisan swings that are increasingly correlated across districts. Second, malapportionment was reduced by almost half in 1994, meaning that rural votes are now worth fewer seats. As a result, parties that can attract swing voters nationally are better positioned for victory than those with a narrow regional base.
