Duplicates in the original directed dyad-year alliance data were pre-processed. Check
cow_alliance
in the package's data-raw
directory on Github for more information.
This function will also work with leader-dyad-years, though users should be careful with leader-level
applications of alliance data. Alliance data are primarily communicated yearly, making it possible---even
likely---that at least one leader-dyad in a given year is credited with an alliance that was not active in the particular
leader-dyad. The Correlates of War's alliance data are not communicated with time measurements more granular than
the year. Apply these data to leader-level analyses with that in mind.