Why do democracies break down? This question is at the heart of contemporary concern about the prospects for democracies around the world. The question also has a long tradition in the history of political thought, and from this long history, we can take away two ways of thinking about what is driving the current crisis of democracy. Is it cultural, a consequence of changing norms? Or is it institutional, a problem in the way our political systems divide power and channel conflict? We’ll look closely at these alternative explanations and at the methods that Political Scientists are developing to measure democratic breakdown and validate competing theories.