I'd say that the above summary of the article is incorrect. The article poses that a strong, central state is essential for the elimination of clan structures as the fundamental organizing principle of a society. It also states that the concept of individual liberty we have today could only develop under such strong, central states, and that strong, central states are essential to the preservation of that liberty. The 'natural' inclination of any society is to gravitate back towards clannish behavior, and the role of the state is to prevent that kind of back-sliding.

The key in this story is not the development of modern democracies, but the development of strong, central states that superseded clan structures, regardless of how liberal those strong governments actually are. While the author doesn't state this explicitly, the reason is that conflicts in these cases are not decided by clan strength, but rather by a (nominally) impartial, superior party -- whether that's the rule of law or the arbitrary decisions of a ruler.

In that sense, the definition of a strong, central state becomes any institution that rules the clans without being (too) influenced by their relative strength, and that is not beholden to clan politics for its power. This does fit with a lot of the historical knowledge we have.