the Treaty of Leipzig. A collateral line of the Wettin princes received what later became Thuringia and founded several small states there (see Ernestine duchies). Since these princes were allowed to use the Saxon coat of arms, in many towns of Thuringia, the coat of arms can still be found on historical buildings. The remaining Saxon state became still more powerful, also incorporating new territories and was known in the 18th century for its cultural achievements, although it was politically weaker than Prussia and Austria, states which oppressed Saxony from the north and south, respectively. Between 1697 and 1763, the Electors of Saxony were also elected Kings of Poland in personal union. In 1756, Saxony joined a coalition of Austria, France and Russia against Prussia. Frederick II of Prussia chose to attack preemptively and invaded Saxony in August 1756, precipitating the Third Silesian War (part of the Seven Years' War). The Prussians quickly defeated Saxony and incorporated the Saxon army into the Prussian army. At the end of the Seven Years' War, Saxony recovered its independence in the 1763 Treaty of Hubertusburg. 19th century In 1806, French Emperor Napoleon abolished the Holy Roman Empire and established the Electorate of Saxony as a kingdom in exchange for military support. The Elector Frederick Augustus III accordingly became King Frederick Augustus I of Saxony. Frederick Augustus remained loyal to Napoleon during the wars that swept Europe in the following years; he was taken prisoner and his territories declared forfeit by the allies in 1813, after the defeat of Napoleon. Prussia intended the annexation of Saxony but the opposition of Austria, France, and the United Kingdom to this plan resulted in the restoration of Frederick Augustus to his throne at the Congress of Vienna although he was forced to cede the northern part of the kingdom to Prussia, which led to the loss of nearly 50% of the Saxon territory. Most of these lands were merged with the Duchy of Magdeburg, the Altmark and some smaller territories to become the Prussian Province of Saxony, a predecessor of the modern state of Saxony-Anhalt. Lower Lusatia and part of the former Saxe-Wittenberg territory became part of the Province of Brandenburg and the northeastern part of Upper Lusatia became part of the Province of Silesia. The rump Kingdom of Saxony had roughly the same extent as the present state, albeit slightly smaller. Meanwhile, in 1815, the southern