To insure the stability of the federal union thus formed, the
Constitution created a "system of United States courts extending
throughout the states, empowered to define the boundaries of federal
authority, and to enforce its decisions by federal power." This
omnipresent federal judiciary was undoubtedly the most important
creation of the statesmen who framed the Constitution. The closely-knit
relations which it established between the states contributed powerfully
to the growth of a feeling of national solidarity throughout the whole
country. The United States today cling together with a coherency far
greater than the coherency of any ordinary federation or league. Yet the
primary aspect of the federal Constitution was undoubtedly that of a
permanent league, in which each state, while retaining its domestic
sovereignty intact, renounced forever its right to make war upon its
neighbours and relegated its international interests to the care of a
central council in which all the states were alike represented and a
central tribunal endowed with purely judicial functions of
interpretation. It was the first attempt in the history of the world, to
apply on a grand scale to the relations between states the same legal
methods of procedure which, as long applied in all civilized countries
to the relations between individuals, have rendered private warfare
obsolete. And it was so far successful that, during a period of
seventy-two years in which the United States increased fourfold in
extent, tenfold in population, and more than tenfold in wealth and
power, the federal union maintained a state of peace more profound than
the _pax romana._

Twenty years ago this unexampled state of peace was suddenly interrupted
by a tremendous war, which in its results, however, has served only to
bring out with fresh emphasis the pacific implications of federalism.