Accordingly, the First Silesian War (1740–1742, part of the War of the Austrian Succession) began on 16 December 1740 when Frederick invaded and quickly occupied almost all of Silesia within seven weeks. Though Frederick justified his occupation on dynastic grounds, the invasion of this militarily and politically vulnerable part of the Habsburg empire also had the potential to provide substantial long-term economic and strategic benefits. The occupation of Silesia added one of the most densely industrialised German regions to Frederick's kingdom and gave it control over the navigable Oder River. It nearly doubled Prussia's population and increased its territory by a third.