In order to render my subject manageable, I have excluded from it the literature dealing with legal history, with the general history of political ideas, and with the constitutional and political debates that preceded and accompanied the American Revolution. Each of these is a large subject in itself and would, require for its most summary treatment a separate paper. I limit myself to what has been written during the last fifty years or so about the constitutional history of the Union and of the states in their relation to the Union since the year 1783.