Alliances have been credited with preventing wars and provoking wars, and they have been important instruments of statecraft for centuries. This data set records all formal alliances among states between 1816 and 2000, including mutual defense pacts, non-aggression treaties, and ententes. The Correlates of War Formal Alliance data set seeks to identify each formal alliance between at least two states that fall into the classes of defense pact, neutrality or non-aggression treaty, or entente agreement. A defense pact (Type I) is the highest level of military commitment, requiring alliance members to come to each other’s aid militarily if attacked by a third party. As the labels imply, neutrality and non-aggression pacts (Type II) pledge signatories to either remain neutral in case of conflict or to not use or otherwise support the use of force against the other alliance members. Finally, ententes (Type III) provide for the least commitment and obligate members to consult in times of crisis or armed attack. Each alliance classifies the highest level of military support that an alliance member pledges to another alliance member. The data set provides the type, members, and appropriate dates of activity of each identified alliance.

Version 3 of the alliance data sets updates the collection to include the years 1816-2000. In addition to extending to 2000, changes were made to the prior data set, both in the inclusion of additional alliances and the exclusion of some old alliances. Users of the data are urged to familiarize themselves with the basic coding procedures employed in the generation of the data. Distributed data include both the list of alliances and a dyadic conversion allowing easy incorporation into dyad-year analyses.

In any papers or publications that utilize this data set, users are asked to give the version number and cite the article of record for the data set, as follows:
Bibliography Entry: Gibler, Douglas M., and Meredith Sarkees. Forthcoming. "Measuring Alliances: the Correlates of War Formal Interstate Alliance Data set, 1816-2000." Journal of Peace Research.

The original alliance data set was assembled in the 1960s under the auspices of the COW project and was initially discussed in:
Singer, J. David, and Melvin Small. 1966. "Formal Alliances, 1815-1939." Journal of Peace Research 3:1-31.

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