  Many social networks exhibit some underlying community structure. In
particular, in the context of historical research, clustering of different
groups into warring or friendly factions can lead to a better understanding of
how conflicts may arise, and whether they could be avoided or not. In this work
we study the crisis that started in 1225 when the Emperor of the Holy Roman
Empire, Frederick II and his son Henry VII got into a conflict which almost led
to the rupture and dissolution of the Empire. We use a spin-glass-based
community detection algorithm to see how good this method is in detecting this
rift and compare the results with an analysis performed by one of the authors
(Gramsch) using standard social balance theory applied to History.
