Nils Weidmann at Princeton University and Kristian Skrede Gleditsch at the University of Essex has constructed this historical border dataset. The cShapes package includes all state border changes from 1946 and onward. It provides an excellent dataset to visualize border changes, in addition to construct historical data. The dataset is available both as an R package, and shapefile format.
See Nils Weidmann’s webpage for more information