The Austrian statesmen were willing enough to negotiate, but they clung to the gains which they had made. Their preparations for war were not complete, but they did not believe that Prussia meant to fight. Both sides, indeed, hoped more from negotiation than from battle. It became evident, too, that Frederick was no longer the general whose delight was in swift and resolute movements. Not till April 6, 1778, did he march from Berlin, and then he drew rein in southern Silesia, and spent three months more in fruitless haggling. At last, on July 3rd, he made a declaration of war, and two days later completed his march across the mountains into Bohemia. Even then the Queen brought herself to beg for peace, so that, although hostilities continued, August was half gone before the diplomatists finally dispersed.
The War of the Bavarian Succession formally began, however, when Frederick set out for Bohemia, on July 3, 1778. He was attacking with two armies, each about 80,000 strong. Earlier in the year he had hoped that the main Austrian force would assemble in Moravia. In that case his plan was to lead his own army from Silesia against it, to win a great victory, and thus to compel the enemy to call back their troops from Bohemia. This would make it easy for Prince Henry with a combined host of Prussians and Saxons to advance on Prague while the King made progress in Moravia. The two armies, if all continued to go well, would then press forward towards the Danube.
The plan was spoiled, however, because the Austrians were bold enough to choose north-eastern Bohemia for their place of concentration. There they were indeed further from Vienna, but they secured greater possibilities of offensive action. If Frederick invaded Moravia they could overrun Silesia behind his back or fall upon Prince Henry and Saxony in overwhelming force. The King, therefore, reluctantly turned aside into Bohemia by way of Nachod in order to engage the enemy’s attention until his brother, marching from Dresden, should have established himself firmly in the north.
On his arrival in Bohemia, Frederick found the Austrians some 250,000 strong. Joseph and Lacy with the bulk of the troops confronted him in a position on the Elbe nearly fifty miles in length and as strong as water, earthworks, and cannon could make it. Judging it impregnable, Frederick waited impatiently for his brother to get the better of Laudon, who was guarding the northern gate into Bohemia. The army chafed at the enforced inaction, but the King still hoped by sending repeated detachments to Moravia to compel the enemy to meet him there in the field.
Prince Henry, after hesitating for some time between different routes, performed his task to perfection. Early in August he led his army over the mountains to the east of the Elbe by ways hitherto reputed impassable. Laudon was at his wits’ end. He fell back upon the line of the Iser, but on August 14th, Joseph himself admitted that he was too weak to hold it. If Laudon were driven off, the great position on the Elbe would be untenable, but Prince Henry lacked the hardihood to venture the decisive move. Dissensions between the royal brothers and the failure of their efforts to effect a junction justified the policy of their opponents, who, Frederick sneered, seemed to be turned into stone. Soon the movements of the Prussians were dictated largely by hunger and the conflict earned its nickname of the Potato War. Heavy rains completed their discomfiture. By the middle of October the exultant Austrians had seen the last of the invaders.
The campaign of 1778 cost the combatants some 20,000 men and 29,000,000 thalers in money. Frederick had shown himself captious and irresolute. His brother declared that he was more on his guard against the treachery of the King than against the enterprises of the enemy. The army had become dejected, ill-disciplined, and disaffected. Frederick, though he prepared to invade Moravia in the spring, spent the winter in working his hardest for peace. France and Russia lent their aid. In March, 1779, a congress of the four Powers met at Teschen, and on May 13th peace was signed.
The Peace of Teschen was in some degree a triumph for Frederick. The chief points for which he had taken up arms were secured at no great cost. The Austrian acquisitions were limited to the Quarter of the Inn, a strip of territory bounded on the west by that river, while Bavaria was obliged to pay 4,000,000 thalers in settlement of the Saxon claims. Prussia seemed thus to have maintained the rights of two great German princes from motives of pure patriotism. Her military prestige, on the other hand, had suffered. She had not derived prompt support from her intimacy with Russia and she had failed to disturb the connexion between Austria and France. No less than four royal marriages now linked the Bourbons to their secular foes the Hapsburgs. By accepting the guarantee of France and Russia to a treaty in which the Peace of Westphalia was once more confirmed, Prussia had moreover paved the way for unwelcome foreign intrusions into German affairs.
Frederick saw good reason to fear that the danger from Austria would be renewed so soon as Joseph should be emancipated from the restraining influence of the aged Queen. For the time being, however, he was free to resume his round of toil, to mourn the loss of Voltaire, to correspond with the philosopher d’Alembert, and to pursue reforms in law and education. The Prussian judges were now empowered to interrogate the parties to suits and compelled to hear what they had to say. A codification of the law and a Book of Rights which should stereotype the existing feudal system of society in Prussia were set on foot. And at the moment when Romanist sovereigns drove out the Jesuits, Frederick welcomed the fugitives as harmless individuals, who could help to supply one of the most pressing needs of the State by instructing the common people.
The lack of qualified elementary teachers in Frederick’s dominions was attested by the fact that in 1763 an edict of educational reform in Silesia permitted them to continue such employments as tailoring, but forbade them to eke out their incomes by peddling, by selling beer or brandy, or by fiddling in public-houses. A counsel of despair had been to set the worn-out sergeants to keep school. Out of 3443 of them, however, only 79 were reported by the military officials as possibly fit to serve, and investigation by the civil authorities still further reduced the number. Under such conditions as these the influx of members of an order which had long been famous for its schools was regarded by the King as a boon to Prussia. To grant them an asylum gratified his real love of toleration, without in his opinion involving the smallest peril to the allegiance of his subjects.
From time to time, however, Frederick was unpleasantly reminded of his insecurity. In the summer of 1780, Austria secured a portion of the Bavarian inheritance which it was beyond his power to take away. In spite of all his diplomacy, the mighty sees of Cologne and Münster fell into Hapsburg hands. At this moment of triumph, Maria Theresa died (November 29, 1780). “She has done honour to her throne and to her sex,” wrote the King to d’Alembert. “I have made war against her, but I have never been her enemy.”