Peace is not the mere absence of war or the simple maintenance of a balance of power between forces, nor can it be imposed at the dictate of absolute power. It is called, rightly and properly, a work of justice. It is the product of order, the order implanted in human society by its divine founder, to be realized in practice as men hunger and thirst for ever more perfect justice. The common good of the human race is subject to the eternal law as its primary principle, but its requirements in practice keep changing with the passage of time. The result is that peace is never established finally and for ever; the building up of peace has to go on all the time. Again, the human will is weak and wounded by sin; the search for peace therefore demands from each individual constant control of the passions, and from legitimate authority untiring vigilance.