These are the Correlates of War major powers data.
Format
A data frame with 14 observations on the following 8 variables.
ccodea numeric vector for the Correlates of War country code
styearthe start year as a major power
stmonththe start month as a major power
stdaythe start day as a major power
endyearthe end year as a major power
endmonththe end month as a major power
enddaythe end day as a major power
versiona version identifier
Details
Data are provided "as-is" with no additional re-cleaning before inclusion into this data set (beyond eliminating the state abbreviation).
References
Correlates of War Project. 2017. "State System Membership List, v2016." Online, https://correlatesofwar.org/data-sets/state-system-membership/