This data set records the fluctuating composition of the state system since 1816. It also identifies countries corresponding to the standard Correlates of War country codes.
State System Membership
Overview
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 2024 extends the temporal domain of the collection through December 2024.
The Correlates of War project considers a political entity to be a state and member of the interstate system from 1816-2024 if it meets 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.
Citation
We ask users of the data sets to cite this data set as follows:
Correlates of War Project. 2025. “State System Membership, v2024.” Online, https://correlatesofwar.org
Data Sets
The files associated with the interstate system membership can be obtained in .csv or .dta formats. The first line of each data file is a header record containing the variable names.
Questions and Feedback
The data sets associated with the state system are hosted by Jeff Carter (Appalachian State University) and Scott Wolford (University of Texas at Austin). Questions about these data sets may be emailed to Jeff Carter (jtc475@gmail.com) or Scott Wolford (swolford@austin.utexas.edu).
State System Codebook
Describes the content and formate of the data, and provides details of the operational criteria for state system membership.
State System Membership Codebook.pdf
State System FAQ
Contains answers to some FAQs about the state system membership datasets
States
Provides the entry and exit dates of states, country codes, and abbreviations.
State System Membership Datasets
Major Powers
Provides the entry and exit dates for states to be designated as major powers
State System Data
Provides a blank country-year dataset of all members of the system in each year.
Non-Directed Dyad-Year Data
Provides a blank non-directed dyad-year dataset of all dyads in the system in each year.
Non-Directed Dyad-Year Datasets
Directed Dyad-Year Data
Provides a blank directed dyad-year dataset of all dyads in the system in each year.