This book asks and answers the question, how has nationalization influenced US elections across different political eras? It looks at historical variation in nationalization through an analysis of congressional elections from 1840 to 2020. By examining roughly 180 years of elections, the authors leverage considerable differences in electoral competition, electoral rules, nationalization, polarization, and partisan advantage via the incumbency advantage. Moreover, Carson, Sievert, and Williamson employ a unique survey design to capture citizen attitudes toward the nationalization of politics to further consider the question of how nationalization is currently shaping politics.