Scholars and pundits have offered a wide variety of other possible causes of the polarization of the last half century, but much less attention has been given to the long trend toward depolarization in the first half of the twentieth century, and many of the proffered explanations fit poorly with the actual history of party politics in that period. In fact, even for the later period of increasing polarization after 1970, evidence in support of many putative causal factors is weak.
