With the bulk of the Austrian army occupied in Eastern France, Frederick launched the Second Silesian War on 15 August, and by the end of the month, all 80,000 of his troops were in Bohemia. Although Maria Theresa's main objective was to regain Silesia, the speed of the Prussian advance took them by surprise. On 23 August, Prince Charles withdrew from Alsace to defend Bohemia, with little interference from the French due to Louis' illness.