The United States Constitution established the world’s first federal system encompassing an economic union and a political union whose central characteristic is dual sovereignty with Congress possess- ing delegated powers and states possessing reserved or residual powers. A federal system automatically raises questions pertaining to the nature of appropriate relations between the national government and state gov- ernments at the boundary lines of their respective authority and between sister states each possessing equal powers. Relations between states in such unions may be cooperative, competitive, and/or conflictive in gen- eral and with respect to taxation of interstate commerce in particular
