This text argues against the grain of many late-20th-century theories in political science by explicitly discussing when and how ideas influence political behaviour; exploring the German and Swedish Social Democrat Movements during the interwar period. Even though German and Swedish social democrats belonged to the same transnational political movement and faced similar political and social conditions in their respective countires before and after World War I, they responded very differently to the challenges of democratization and the Great Depression - with far-reaching consequences for the fates of the countries and the world at large. Explaining why these two social democratic parties acted so differently is the primary task of this book. Sheri Berman's answer is that they had very different ideas about politics and economics - what she terms programmatic beliefs. The Swedish Social Democrats placed themselves at the forefront of the drive for democratization and a decade later responded to the Great Depression with a bold economic programme, using it to build a period of political hegemony. The German Social Democrats, on the other hand, had democracy thrust upon them and then dithered when faced with economic crisis; their haplessness clearing the way for a bolder and more skillful political actor - Adolf Hilter.