In recent years, developed Western democracies have seen the rapid rise of new political forces, including movements commonly described as “populist”, “nationalist” or “sovereigntist”, but also new forms of opposition against these movements. A growing body of research identifies these changes as the product a realignment driven by the differential impact of globalization on these societies. In this dissertation, I build on this research by arguing that geography plays a key role in shaping this realignment. The benefits of globalization tend to concentrate in large metropolitan areas, while the rest of the country bears the brunt of its negative effects. As a result, developed democracies see the rise of a political cleavage opposing these two geographic entities, with large urban areas increasingly distinguishing themselves from less-dense communities in their voting patterns and other political behaviors. I test this argument by examining geographic variations in socioeconomic and electoral patterns in four major developed democracies: France, Germany, the United Kingdom and the United States. I find clear evidence for this dynamic in three countries, with Germany presenting some null findings. Complementing the geographic analysis, I also examine individual-level attitudes and behavior through recent, high-quality survey data from the United States. This data reveals that the political cleavage between large urban areas and the rest of the country persists even when controlling for individual socioeconomic characteristics. This research sheds light on a major transformation in Western politics, which has already resulted in stunning electoral upsets with major repercussions for world politics.