The Evolution of Party Unity: A New Approach Through Legislative Debates

How has the internal unity of political parties evolved, both historically and currently? Do parties of the present see less internal dissent than previously in history? These questions have interested political science for long. Generally, scholars have explored this by looking at voting cohesion. But since voting cohesion inside parties has been very high for many decades, this approach gives little variability with which to actually study party unity. This paper, instead, argues that legislative debates offer a great and so far mostly unused source of information on the evolution of party unity. Within parliamentary speeches, there is much more variability that we can use to investigate party unity for more than a century. And through artificial intelligence, we now also have the tools necessary to do this on a large scale. The paper demonstrates this on a new dataset of Danish parliamentary debates spanning from the early 20th century until today. This approach opens a new frontier for the study of party unity.