The position of affairs may be simply stated. Two Austrian armies were in the field, one conquering Bavaria, the other protecting it against an attack from the side of Bohemia, where the allies were still masters of Prague. If this second army were driven back by a superior force, the first would be recalled to support it. Thus Bavaria and Bohemia, the actual and the pretended inheritance of Charles Albert, would be freed from the Austrians together. At the same time the French in Bohemia would be relieved from the fear of being outnumbered and attacked, and the Saxons would have the simplest march possible—straight into Bohemia by the natural highroad of the Elbe. Every military consideration thus summoned Frederick to join in clearing the kingdom of Austrian troops. But this plan promised no special advantage for the King of Prussia and it opened no market in which he might barter his allies. With infinite labour he therefore secured the adoption of another, in which these defects were remedied. This was that he should lead the Saxon army into Moravia to assist the Prussians in conquering the province, and in thus creating a diversion which, he maintained, would aid the Emperor as well as any other.
The Saxons reluctantly left their country with no force, save the French, to guard its frontier against the Austrian army of Bohemia. Frederick was therefore secure against treason on his flank and could again stir the waters of politics in full confidence that his House would gain some profit. Moravia might become to Silesia what Silesia had now become to Brandenburg—a dependency and an outwork. Or if this was too much to hope for, he as conqueror of Moravia might at least dictate to Vienna the surrender of a Silesia augmented by cuttings from the Bohemian kingdom, of which Frederick regarded the Emperor or the Queen as lawful sovereign exactly according to his convenience at the moment. At the worst Moravia might pass to the Saxon House, which was a weaker and therefore a safer neighbour than the Hapsburg.
All these calculations were falsified by events. The invasion of Moravia was a far more difficult task than the invasion of Silesia. Instead of a level and fertile country inhabited in part by Protestant well-wishers, Frederick found a rugged desert whose people hated the Prussians and did them every mischief in their power. He devastated the land by way of penalty, and dragged the grumbling Saxons through clouds of guerillas to Brünn, the capital, where he induced them to join him in a siege. As leader of a composite army, however, he was no longer served with the prompt and unquestioning obedience which the unmixed Prussian forces had displayed.