Complex sentence: During the Franco-Prussian War the line received great strategic importance as a supply route and as a result the building of the Sieg bridge was accelerated with extra workers, starting in the late summer of 1870.
Split into simpler sentences: During the Franco-Prussian War, the line was of great strategic importance as a supply route. As a result the building of the Sieg bridge was accelerated with extra workers, starting in the late summer of 1870.