  While a large number of informal factors influence how people interact,
modern societies rely upon law as a primary mechanism to formally control human
behaviour. How legal rules impact societal development depends on the interplay
between two types of actors: the people who create the rules and the people to
which the rules potentially apply. We hypothesise that an increasingly diverse
and interconnected society might create increasingly diverse and interconnected
rules, and assert that legal networks provide a useful lens through which to
observe the interaction between law and society. To evaluate these
propositions, we present a novel and generalizable model of statutory materials
as multidimensional, time-evolving document networks. Applying this model to
the federal legislation of the United States and Germany, we find impressive
expansion in the size and complexity of laws over the past two and a half
decades. We investigate the sources of this development using methods from
network science and natural language processing. To allow for cross-country
comparisons over time, we algorithmically reorganise the legislative materials
of the United States and Germany into cluster families that reflect legal
topics. This reorganisation reveals that the main driver behind the growth of
the law in both jurisdictions is the expansion of the welfare state, backed by
an expansion of the tax state.
