Students of world politics disagree about the approaching outlook for war. Are we in the midst of an era of peace with a declining prospect of war, or are we facing a future characterized by increasing “ethnic” conflicts? This puzzle has led scholars to call for a more comprehensive examination of the phenomenon of war. A discussion concerning this need for a new look at war had also arisen within the Correlates of War Project. For more than three decades the Correlates of War Project's database has served the research needs of most of the quantitative world politics community, especially in identifying and trying to account for several classes of war (inter-state, extra-systemic, and civil) throughout the international system since 1816. However, a number of the disagreements in the literature concerning the prospects of war derive from the tendency of many researchers to rely on only one of our data sets (e.g., inter-state war). Here we wish to stimulate a broader view of war by examining the interplay among the three major types of war.
Historical developments of the past half-century, and especially since the end of the Cold War, have rendered the original COW war typology increasingly incomplete. Consequently, we developed a modified typology of war and attempted to format the descriptive variables in ways that would facilitate a more comparative and comprehensive analysis of warfare. While the reader should be reassured that Inter-state Wars remain as previously defined, we introduce the term “Intra-state War” in place of our original Civil War category, and the term “Extra-state War” in place of our initial Extra-systemic War category, allowing us to reclassify several such wars. This revised typology coupled with an update of the data allows us to take a fresh look at the question whether, from the perspective of the past two centuries, war is in fact becoming less common. The article concludes with a series of analyses that describe the patterns and trends of all types of war––reflecting the new typology––since the Congress of Vienna. These analyses reflect a disquieting constancy in warfare and hint at patterns of interchangeability or substitutability among the types of war.