Physiocracy was the first attempt to describe an economy as a system rather than a policy problem, and the first to draw the conclusion that it should mostly be left alone.
Quesnay, physician to Louis XV, built the Tableau économique (1758) as a circulation diagram in the manner of the blood: value moves between the productive class of cultivators, the proprietors, and the "sterile" class of artisans and merchants, who transform matter without adding to the total. Only land yields a produit net — a surplus over the cost of production — so agriculture is the sole source of new wealth, and all taxation should fall on the landowner in a single tax, every other levy being merely passed along.
The economics is wrong and the method is decisive. Treating the economy as an interdependent circular flow, with equilibrium conditions and a reproducible surplus, is the move that makes economics a science, and both Marx and the input-output tradition acknowledged the Tableau as an ancestor.
The politics is "legal despotism": a sovereign undivided in power but wholly bound by a natural order he does not author and cannot alter. This is where the school's famous slogan comes from — laissez faire, laissez passer — and where its interest in China comes in. Quesnay read the Jesuit accounts as evidence that a great empire had already been governed on these principles for millennia, and Le Despotisme de la Chine (1767) made the argument at length; contemporaries called him the Confucius of Europe. Turgot, as controller-general, briefly attempted the program in office and was destroyed by the resistance.