Contrary to the view of state governments as constrained and marginal actors, this study reveals their increasing influence on U.S. public policy.

Issue Analysis: Examines 16 key policy areas spanning 45 years (1970-2014).

* Growing interstate variation in policies like taxation and abortion rights means state location now significantly shapes lived experiences.

* Policy polarization—a divergence between Democratic and Republican state outcomes—has dramatically increased post-2000 across most areas.

Core Finding: Party control strongly predicts policy differences in 14 out of the 16 areas by the late 20th century, with this predictive power increasing substantially after 2000.

Policy Implication: This enhanced analysis shows party dominance's significant impact on state-level outcomes, particularly in domains like healthcare where polarization is pronounced.