I'm very interested in the various systems of government and society that have been popular throughout history: tribalism, feudalism, democracy/capitalism, and the transitions between them.
I'm interested if there are any newspaper articles, letters, books, etc. that discussed these revolutions and new systems of governance. What was the overall reaction (criticisms and praises) to what would become our current system of governance?
One thing that's important to remember is that the United States and the French Republic were not the first republics in the world, nor even the first republics in the "modern" world. Even if you exclude ancient republics like Rome and Athens, educated Europeans were well aware of examples of contemporary and recent republics. You had the Dutch Republic, the Swiss Confederation and the recent experience of the English Commonwealth, plus the long and venerable traditions of Italian republics like Venice, Genoa and (more periodically) Florence, and a range of city-state Republics in Germany, of which the most prominent might be the cities that unified into the Hanseatic League.
The England of the late 18th Century was also seen as not especially feudal, though it remained a monarchy. Historians like Lord Kames put forth a model of history in which human civilization advanced through four stages. The first three were hunter-gatherers, pastoralists and farmers. But the fourth, which England was widely acknowledged to be in, was "commercial society" — very distinct from the feudal agricultural model.
What was unique about America and France for their time was the scale of their republics — not mere city-states or leagues of city-states, France and especially America were vast nations with millions of inhabitants; every successful republic prior to them had been small, the only examples of large-scale republics, like the English Commonwealth or ancient Rome, had fallen. It was with that context that Madison wrote the famous Federalist #10, which took the then-counter-intuitive position that the sheer size of the United States would, with the proper constitution, help it endure.
The smaller the society, the fewer probably will be the distinct parties and interests composing it; the fewer the distinct parties and interests, the more frequently will a majority be found of the same party; and the smaller the number of individuals composing a majority, and the smaller the compass within which they are placed, the more easily will they concert and execute their plans of oppression. Extend the sphere, and you take in a greater variety of parties and interests; you make it less probable that a majority of the whole will have a common motive to invade the rights of other citizens; or if such a common motive exists, it will be more difficult for all who feel it to discover their own strength, and to act in unison with each other. Besides other impediments, it may be remarked that, where there is a consciousness of unjust or dishonorable purposes, communication is always checked by distrust in proportion to the number whose concurrence is necessary.
That argument was made against the assumption that republican government could only endure on a small scale, where the citizens all knew each other, and that large countries populated by strangers required autocracies. But this assumption that Madison was arguing against was premised on an analysis of numerous actual, existing republics, some of which had endured and others had collapsed. The idea of republican government was not novel. As Madison writes:
The instability, injustice, and confusion introduced into the public councils, have, in truth, been the mortal diseases under which popular governments have everywhere perished; as they continue to be the favorite and fruitful topics from which the adversaries to liberty derive their most specious declamations. The valuable improvements made by the American constitutions on the popular models, both ancient and modern, cannot certainly be too much admired... (emphasis added)
Again, the assumption was that there were numerous models of republican government, "both ancient and modern." The problem was not that no one knew what republican government looked like, it was that too many republics had fallen into tyranny.
Others can perhaps weigh in with more detail on the specific reactions to the American and French republics as they emerged.
Sources: