About the first pandemic, when bubonic plague ravaged Europe six centuries before the Black Death.

Eventually. He started out with background. Deep background. In fact, it took more than half of the book before the first flea appeared. A short, but intense, description of the effects of the plague in Constantinople, followed by a great deal of chronological leaps, as he then raced through the following centuries, touching down here and there as the plague reappeared, detailing how it changed history.

The final conclusion was that it was this appearance of the plague that destroyed the Roman Empire and allowed the rise of the nation-states of Medieval Europe. And also permitted the rise of Islam, as the weakened empire was no longer able to contain it.