By 1743, the Austrians had subdued Bavaria and driven the French out of Bohemia. Frederick strongly suspected Maria Theresa would resume war in an attempt to recover Silesia. Accordingly, he renewed his alliance with France and preemptively invaded Bohemia in August 1744, beginning the Second Silesian War. In late August 1744, Frederick's army had crossed the Bohemian frontier, marched directly to Prague, and laid siege to the city, which surrendered on 16 September 1744 after a three-day bombardment. Frederick's troops immediately continued marching into the heart of central Bohemia. However, Saxony had now joined the war against Prussia. Although the combined Austrian and Saxon armies outnumbered Frederick's forces, they refused to directly engage with Frederick's army, harassing his supply lines instead. Eventually, Frederick was forced to withdraw to Silesia as winter approached. In the interim, Frederick also successfully claimed his inheritance to the minor territory of East Frisia on the North Sea coast of Germany, occupying the territory after its last ruler died without issue in 1744.