Frederick II., a young, ambitious and energetic sovereign, longed not only to add to his dominions but to play a great part in European politics. His father had guaranteed the pragmatic sanction, but as the conditions on which the guarantee had been granted had not been fulfilled by Charles VI., Frederick did not feel bound by it, and revived some old claims of his family on certain Silesian duchies. Maria Theresa would not abate her rights, but before she could assert them Frederick had entered Silesia and made himself master of it. Meanwhile, the elector of Bavaria had come forward and disputed Maria Theresa's right to the succession, and the elector of Saxony had also put in a claim to the Austrian lands. Taking advantage of these disputes, France formed an alliance with the two electors and with the king of Prussia against Austria; and in the war which followed the allies were at first so successful that the elector of Bavaria, through the influence of France, was crowned emperor as Charles VII. (1742-1745). Maria Theresa, a woman of a noble and undaunted spirit, appealed, with her infant son, afterwards Joseph II., in her arms, to the Hungarian diet, and the enthusiastic Magyars responded chivalrously to her call. To be more at freedom she concluded peace with Frederick, and ceded Silesia to him, although greatly against her will. Saxony also was pacified and retired from the struggle. After this Maria Theresa, supported by England, made way so rapidly and so triumphantly that Frederick became alarmed for his new possessions; and in 1742 he once more proclaimed war against her, nominally in aid of the emperor, Charles VII. Ultimately, in 1748, she was able to conclude an honourable peace at Aix-la-Chapelle; but she had been forced, as before, to rid herself of Frederick by confirming him in the sovereignty of the territory he had seized.
After the death of Charles VII., Francis, grand duke of Tuscany, Maria Theresa's husband, was elected emperor. Francis I. (1745-1765), an amiable nonentity, with the instincts of a shopkeeper, made no pretence of discharging important imperial duties, and the task of ruling the hereditary possessions of the house of Habsburg fell wholly to the empress-queen. She executed it with discretion and vigour, so that Austria in her hands was known to be one of the most formidable powers in the world. Her rival, Frederick II., was, if possible, still more active. It did not occur to him, any more than to the other German sovereigns of the 18th century, to associate his people with him in the government of the country; he was in every respect a thoroughly absolute sovereign. But he shared the highest ideas of the age respecting the responsibilities of a king, and throughout his long reign acted in the main faithfully as "the first servant of the state." The army he always kept in readiness for war; but he also encouraged peaceful arts, and diffused throughout his kingdom so much of his own alert and aggressive spirit that the Prussians became more intelligent and more wealthy than they had ever before been. He excited the admiration of the youth of Germany, and it was soon the fashion among the petty princes to imitate his methods of government. As a rule, they succeeded only in raising far larger armies than the taxpayers could afford to maintain.