  In 1990, Germany began the reunification of two separate research systems. In
this study, we explore the factors predicting the East-West integration of
academic fields by examining the evolution of Germany's co-authorship network
between 1974 and 2014. We find that the unification of the German research
network accelerated rapidly during the 1990s, but then stagnated at an
intermediate level of integration. We then study the integration of the 20
largest academic fields (by number of publications prior to 1990), finding an
inverted U-shaped relationship between each field's East or West "dominance" (a
measure of the East-West concentration of a field's scholarly output prior to
1990) and the fields' subsequent level of integration. We checked for the
robustness of these results by running Monte Carlo simulations and a
differences-in-differences analysis. Both methods confirmed that fields that
were dominated by either West or East Germany prior to reunification integrated
less than those whose output was balanced. Finally, we explored the origins of
this inverted U-shaped relationship by considering the tendency of scholars
from a given field to collaborate with scholars from similarly productive
regions. These results shed light on the mechanisms governing the reintegration
of research networks that were separated by institutions.
