Our constitutional history started with the States retaining all powers of sovereignty unimpaired, save those conferred upon the National Government. The evolution of the constitutional system has consisted largely in determining the line of demarcation between State and national authority. The cases involved are many and complicated, but there is a fairly good popular understanding of this continuing struggle between these contending sovereignties. Because of better communication and transportation, the constant tendency has been to more and more social and economic unification. The present continent-wide union of forty-eight States is much closer than was the original group of thirteen States.