The data-raw
directory on the project's Github contains
more information about the underlying data that assists in merging in
these codes.
The user will invariably need to be careful and ask why they want these
data included. The issue here is that both have a different composition
and the merging process will not (and cannot) be perfect. We can note
that a case like Gran Colombia is not too difficult to handle (i.e.
CoW does not have this entity and none of the splinter states conflict
with CoW's coding). However, there is greater weirdness with a case like
the unification of West Germany and East Germany. Herein, Correlates of
War treats the unification as the reappearance of the original Germany
whereas Gleditsch-Ward treat the unification as an incorporation of
East Germany into West Germany. The script will not create state-year
or dyad-year duplicates for the Gleditsch-Ward codes. The size of the
original data remain unchanged. However, there will be some year
duplicates for various Correlates of War codes (prominently Serbia
and Yugoslavia in 2006). Use with care. You can also use the
countrycode package. Whether you use this function or the
countrycode package, do not do this kind of merging without
assessing the output.