As indicated in the section on the Ideal Eternal History, Vico sees that history is cyclical. Vico claims that history begins in a barbarism of sense and ends in a barbarism of reflection. The barbarism of reflection is a returned barbarism in which the common sense established by religion through poetic wisdom holding a society together has been broken down by individual interests. The interests are spurred because individuals each think according to their own conceptual scheme without concern for the society, which makes it barbaric.
Vico describes the returned barbarism this way, “such peoples [in the barbarism], like so many beasts, have fallen into the custom of each man thinking only of his own private interests and have reached the extreme delicacy, or better of pride, in which like wild animals they bristle and lash out at the slightest displeasure (NS 1106).” These private interests lead into a civil war in which everyone betrays everyone else. This takes humanity back to where it started -- individual giants acting solely on their own individual passions.
Vico holds that the barbarism of reflection (which he also calls the 'barbarism of the intellect') is worse than the barbarism of sense; the barbarism of sense, what we usually think of savagery, has 'generous fierceness' -- while it's a state of war of all against all, it's of the kind against which you can fight back or from which you can run away. But the barbarism of reflection has 'vile fierceness' -- it's a war of all against all in which people speak soft words and play innocent out of malice and cunning. There are no more fair fights, because the preferred weapon is the poisoning of social relations. It is the corruption and then the dissolution of the senso commune that binds the community together.