I have updated the Correlates of War Formal Interstate Alliance Data to include the years 1816 to 2012.  Below you can find versions of the data in either Excel or Stata format.  Please do consult the release notes included with each download for both significant dataset changes and variable descriptions.  Please report any dataset questions or found errors to me at dmgibler(at)ua.edu.  I post revisions to the dataset every so often and include those suggestions.

Official download page and support through the Correlates of War Project can be found at http://www.correlatesofwar.org/COW2%20Data/Alliances/alliance.htm

• Release notes and Version 4 change history
• Data in comma-separated files
• Data in Stata format
• List of cases considered for dataset but excluded

Users of this data should cite: 
Gibler, Douglas M. 2009. International military alliances, 1648-2008. CQ Press.