Logistics was a recurring problem for the Russians throughout the war. The Russians lacked a quartermaster's department capable of keeping armies operating in Central Europe properly supplied over the primitive mud roads of eastern Europe. The tendency of Russian armies to break off operations after fighting a major battle, even when they were not defeated, was less about their casualties and more about their supply lines; after expending much of their munitions in a battle, Russian generals did not wish to risk another battle knowing resupply would be a long time coming. This long-standing weakness was evident in the Russian-Ottoman War of 1735–1739, where Russian battle victories led to only modest war gains due to problems supplying their armies. The Russian quartermasters department had not improved, so the same problems reoccurred in Prussia. Still, the Imperial Russian Army was a new threat to Prussia. Not only was Frederick forced to break off his invasion of Bohemia, he was now forced to withdraw further into Prussian-controlled territory. His defeats on the battlefield brought still more opportunistic nations into the war. Sweden declared war on Prussia and invaded Pomerania with 17,000 men. Sweden felt this small army was all that was needed to occupy Pomerania and felt the Swedish army would not need to engage with the Prussians because the Prussians were occupied on so many other fronts.