Military interventions are a common element of wars between and within states. Yet, there is no agreement about how these two phenomena are related and about how to define and code interventions. Departing from the assumption that incorporating military interventions into the scientific study of war allows us to better assess the qualitative transformations of violence over time, we present and compare empirical developments and discuss different concepts of military interventions. In addition, we present our data on wars worldwide for the period from 1990 to 2008 and discuss in more detail the trends and events for 2008