The American Revolution can certainly be labeled radical, as it involved the separation of the American colonies from Great Britain, their mother country, along with the creation of a large-scale democracy based on Enlightenment principles. Keep in mind the larger political context in which the American Revolution was shaped: this was not the modern world where democracy was common; this was an age where monarchy was the norm.
That being said, while the Revolution might be called radical, this does not mean that it did not have its own antecedents. The discourse of the Revolution draws heavily on the older tradition of Resistance Theory, most notably the writings of John Locke, whose own work was shaped by the English Civil War (where he himself wrote to defend the Parliamentarians). That being said, the American Revolution can be considered a dramatic expansion on this earlier discourse, introducing a new context of colonization in order to legitimize the separation between colonies and mother country.
At the same time, you must also factor in the outcome of the American Revolution and the creation of the United States. Again, this was an age where monarchy was the political norm, and creating a democratic government based on Enlightenment principles was an unprecedented political project, one that would influence later revolutions (such as the French Revolution) while shaping the identity of modern democracy.