Laws are rules laid down by the public authority to be observed in society. They ought all to have in view the welfare of the State and of its citizens. Laws which are passed directly in view of the public welfare are public laws; and in this class those which relate to the body itself and the very nature of the society, to the form of government and the manner in which the public authority is to be exercised - those laws which together form the constitution of the State are the fundamental laws.
Civil laws are those which regulate the rights and the conduct of the citizens among themselves. Every Nation that does not wish to fail in its duty to itself must give the utmost care that these laws, and above all the fundamental laws, be established wisely, and in a manner suited to the character of the people and to all the circumstances in which they may happen to be. It must determine them with precision and make them clearly understood, in order that they may possess stability, and neither be eluded nor give rise, if possible, to dissension; so that they to whom the exercise of the sovereign power shall be confided, on the one hand, and the citizens on the other, may equally understand their duties and their rights.
The constitution of a State and its laws are the foundation of public peace, the firm support of political authority, and the security for the liberty of the citizens. But this constitution is a mere dead letter, and the best laws are useless if they be not sacredly observed. It is therefore the duty of a Nation to be ever on the watch that the laws be equally respected, both by those who govern and by the people who are to be ruled by them. To attack the constitution of a State and to violate its laws is a capital crime against society; and if the persons who are guilty of it are those in authority, they add to this crime a perfidious abuse of power confided to them. A Nation must uniformly put down such violations with all the vigor and vigilance which the importance of the case demands. The constitution and laws of a State are rarely attacked from the front; it is against secret and gradual attacks that a Nation must chiefly guard. Sudden resolutions strike men's imaginations; but changes are overlooked when they come about insensibly by a series of steps which are scarcely noted. One would do a great service to Nations by showing from history how many States have thus changed their whole nature and lost their original constitution. The attention of peoples would be awakened. They would not close their eyes to innovations which, though of little account in themselves, serve as so many steps to advance to higher and more disastrous undertakings.
This in an excerpt from The Law of Nations, written by Emmerich de Vattel in 1758. Vattel was a diplomat and one of the most important natural law theorists. His works were frequently used and cited by our founding fathers in their political discourse.