COW Interstate System, 1816-2011


This 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. Version 2011 extends the temporal domain of the collection through December 2011.

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.


We ask users of the data set to cite this data set as follows:

Correlates of War Project. 2011. “State System Membership List, v2011.” Online,

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.


State Codebook 2011.pdf - describes the content and format of the state system membership datasets, and provides details of the operational criteria for state system membership.


State FAQ.pdf - Contains answers to some Frequently Asked Questions about the state system membership datasets.


states2011.csv - provides the entry and exit dates of states, country codes, and abbreviations.


majors2011.csv - provides the entry and exit dates for states to be designated as major powers.


system2011.csv - lists the composition of the state system year by year (providing a blank country-year dataset).

Click here to receive all files in a single zipped data set.

Questions and Feedback

This data set is hosted by Volker Krause, Eastern Michigan University; Phil Schafer, University of Michigan; Karen Ruth Adams, University of Montana. Questions about this data set may be emailed toVolker Krause at