Correlates of War Project

Correlates of War Project

Data Sets of the System


Its data set contains the list of states in the international system as updated and distributed by the Correlates of War Project. These data sets identify states, their standard Correlates of War “country code” or state number (used throughout the Correlates of War project data sets), state abbreviations, and dates of membership as states and major powers in the international system.

The Correlates of War project includes a state in the international system from 1816- 2004 for the following criteria. Prior to 1920, the entity must have had a population greater than 500,000 and have had diplomatic missions at or above the rank of charge d’affaires with Britain and France. After 1920, the entity must be a member of the League of Nations or the United Nations, or have a population greater than 500,000 and receive diplomatic missions from two major powers.

Data Set

The files associated with the interstate system membership data set can be obtained either individually, or in one ZIP file that contains several files. All data files associated with state system membership are in .csv (comma-delimited) format. In this format, values are separated by commas, with string values (e.g. state names) in quotations. The first line of each data file is a header record containing the variable names.

COW Interstate System

The latest official list of all members of the Correlates of War Project’s interstate system, including all major powers, the composition of the system, and all dyads in the system.

Spatial-Temporal Domain: Entire world, 1816-2004
Variables Included: States.csv: COW state abbreviation, number, name, and entry and exit years of statehood; Majors.csv: entry and exit dates of major power status; System.csv: annual composition of the interstate system (one entry per nation-year); Dyads.csv: annual dyadic composition of the interstate system (one entry per nondirectional dyad-year).


The Correlates of War Project was founded in 1963 by J. David Singer, a political scientist at the University of Michigan. The original and continuing goal of the project has been the systematic accumulation of scientific knowledge about war. Joined by historian Melvin Small, the project began its work by assembling a more accurate data set on the incidence and extent of inter-state and extra-systemic war in the post-Napoleonic period. To do this scientifically Singer and Small found they needed to operationally resolve a number of difficult issues such as what is a “state” and what precisely is a “war.” Building upon the work of other pioneers such as Pitirim Sorokin, Lewis Frye Richardson, and Quincy Wright, Singer and Small published The Wages of War in 1972, a work that established a standard definition of war that has guided the research of hundreds of scholars since its publication.

This publication was only the beginning of the project, for the fundamental goal of the project was not just to measure the temporal and spatial variation in war but rather to identify factors that would systematically explain this variation. Accordingly, early efforts were undertaken to measure many of those factors that purportedly accounted for war such as national capability, alliances, geography, polarity, and status in the post-Napoleonic period, and the list of data sets assembled by the project has continued to grow over the years. In addition to the collection of data, the project has conducted many empirical studies about war and conflict. An important progeny of the project is the Behavioral Correlates of War project headed by Russell Leng. Through the years, the project has served as a major training ground for young scholars, and many of today’s best known and widely respected international relations scholars are “products” of the project. More generally, the correlates of war project promoted cumulative science in the field of international relations when the scientific study of politics was in its infancy. By helping to establish a clear temporal and spatial domain for research, promoting the use of clearly defined concepts and common variable operationalizations, and allowing replication of research, the project has been a mainstay of rigorous international relations scholarship.

In the late 1990s scholars became concerned about how the work of the project could be continued given the pending retirement of J. David Singer, and arrangements were made to transfer the project to Penn State under the leadership of Stuart A. Bremer. This transfer was marked by a March, 2001, conference discussing the future study of war, held at Penn State. Penn State has archived all available original material from the Correlates of War project, and is extending and enlarging the data collection efforts it began.

In 2002-2005, the project was led by Interim Director D. Scott Bennett and Associate Director Glenn Palmer. In 2005-2012, Paul Diehl served as project’s Director, and as of January 2013, the project continues under Director Zeev Maoz and Associate Director D. Scott Bennett (who has served in this capacity since 2005).

Source: its website

Further Reading

Palmer, Glenn, Vito D’Orazio, Michael Kenwick, and Matthew Lane. “The MID4 Data Set: Procedures, Coding Rules, and Description.” Conflict Management and Peace Science. Forthcoming.

Maoz, Zeev and Errol A. Henderson. “The World Religion Dataset, 1945-2010: Logic, Estimates, and Trends.” International Interactions 39:265-291.

Braithwaite, Alex. “MIDLOC: Introducing the Militarized Interstate Dispute (MID) Location Dataset.” Journal of Peace Research 47:91-98.

Sarkees, Meredith Reid and Frank Wayman. Resort to War: 1816 – 2007. Washington, D.C.: CQ Press.

Barbieri, Katherine, Omar M. G. Keshk, and Brian Pollins. “TRADING DATA: Evaluating our Assumptions and Coding Rules.” Conflict Management and Peace Science 26:471-491.

Gibler, Douglas M. International Military Alliances, 1648-2008. Washington, D.C.: CQ Press.

Ghosn, Faten, Glenn Palmer, and Stuart Bremer. “The MID3 Data Set, 1993–2001: Procedures, Coding Rules, and Description.” Conflict Management and Peace Science 21:133-154.

Pevehouse, Jon C., Timothy Nordstrom, and Kevin Warnke. “The COW-2 International Organizations Dataset Version 2.0.” Conflict Management and Peace Science 21:101-119.

Stinnett, Douglas M., Jaroslav Tir, Philip Schafer, Paul F. Diehl, and Charles Gochman. “The Correlates of War Project Direct Contiguity Data, Version 3.” Conflict Mangagement and Peace Science 19:58-66.

Tir, Jaroslav, Philip Schafer, Paul Diehl, and Gary Goertz. “Territorial Changes, 1816-1996: Procedures and Data.” Conflict Management and Peace Science 16:89-97.

Jones, Daniel M., Stuart A. Bremer, and J. David Singer. “Militarized Interstate Disputes, 1815-1992: Rationale, Coding Rules, and Empirical Patterns.” Conflict Management and Peace Science 15:163-213.

Gochman, Charles S. “Interstate Metrics: Conceptualizing, Operationalizing, and Measuring the Geographic Proximity of States since the Congress of Vienna.” International Interactions 17:93-112.

Singer, J. David. “Reconstructing the Correlates of War Dataset on Material Capabilities of States, 1816-1985.” International Interactions 14: 115-32.

Singer, J. David, Stuart Bremer, and John Stuckey. “Capability Distribution, Uncertainty, and Major Power War, 1820-1965.” in Bruce Russett (ed) Peace, War, and Numbers, Beverly Hills: Sage, 19-48.

Wallace, Michael, and J. David Singer. “International Governmental Organization in the Global System, 1815-1964.” International Organization 24:239-87.

Small, Melvin, and J. David Singer. “Formal Alliances, 1815-1965: An Extension of the Basic Data.” Journal of Peace Research 6:257-282.

Singer, J. David, and Melvin Small. “Formal Alliances, 1815-1939.” Journal of Peace Research 3:1-31.