Prussia cited its centuries-old dynastic claims on parts of Silesia as a casus belli, but Realpolitik and geostrategic factors also played a role in provoking the conflict.

The valley of the Upper Oder formed a natural military conduit between Brandenburg, the Kingdom of Bohemia and the Margraviate of Moravia, and whichever power held the territory could threaten its neighbours.

[5] After the Catholic victory in the 1621 Battle of White Mountain, the Emperor confiscated Johann Georg's duchy and refused to return it to his heirs after his death, but the Hohenzollerns of Brandenburg continued to assert themselves as the legitimate rulers of Jägerndorf.

[8] As a young prince, Frederick III had secretly agreed to this repossession in return for Leopold's payment of some of his debts,[9] but as monarch he repudiated the agreement and reasserted the old Hohenzollern claims to Jägerndorf and the Silesian Piast heritage.

[16] Frederick saw in Austria's female succession an opportune moment for the seizure of Silesia, calling it "the signal for the complete transformation of the old political system" in a 1740 letter to Voltaire.

[20] The Electorates of Cologne and the Palatinate joined these to form an alliance known as the League of Nymphenburg, which aimed at the diminution or destruction of the Habsburg monarchy and its dominant position among the German states.

Maria Theresa's aims in the conflict were, first, to preserve her hereditary lands and titles and, second, to win or compel support for the election of her husband, Duke Francis Stephen of Lorraine, as Holy Roman Emperor, defending her house's traditional pre-eminence within Germany.

[16] After Emperor Charles's death on 20 October, Frederick quickly resolved to strike first; on 8 November he ordered the mobilisation of the Prussian army, and on 11 December he issued an ultimatum to Maria Theresa demanding the cession of Silesia.

[21] In return, he offered to guarantee all other Habsburg possessions against any attack, pay a large cash indemnity,[22] acknowledge the Pragmatic Sanction, and give his vote as elector of Brandenburg in the imperial election to Maria Theresa's husband.

[23] Strategic warfare in this period centred around control of key fortifications positioned so as to command the surrounding regions and roads, with lengthy sieges a common feature of armed conflict.

Occupied enemy territories were regularly taxed and extorted for funds, but large-scale atrocities against civilian populations were rare compared with conflicts in the previous century.

Neither army acquitted itself well at Mollwitz, and Frederick at one point fled (on Schwerin's advice) to avoid capture, but the Prussians held the field and subsequently portrayed the battle as a victory.

[38] After Austria's failure at Mollwitz to repel the Prussian invasion, other powers were emboldened to attack the beleaguered monarchy, widening the conflict into what would become the War of the Austrian Succession.

[50][51][52] In mid-October, Charles Albert of Bavaria and his French allies were encamped near Vienna, ready to besiege it, but he became concerned that Saxony and Prussia would seize parts of Bohemia, which he had also claimed.

[55] As the Franco-Bavarian allies made territorial gains, Frederick became concerned that Prussia might be sidelined in the eventual peace agreement, so he repudiated the Convention of Klein Schnellendorf, accusing the Austrians of violating its secrecy, and joined the general advance southward into Bohemia and Moravia.

[59] As the Moravian advance collapsed, Charles Alexander of Lorraine (Maria Theresa's brother-in-law) led a reinforced Austro-Hungarian army of 30,000 through Moravia toward Bohemia, hoping to disperse the Prussians and liberate Prague.

[49] The British treasury had financed much of Austria's war effort through cash subsidies meant to weaken France, and Hyndford threatened to withdraw Britain's support if Maria Theresa refused to concede Silesia.

Prussia also agreed to take on some of Austria's debts that had been secured against assets in Silesia, as well as committing to remain neutral for the remainder of the ongoing War of the Austrian Succession.

[66] The First Silesian War ended in a clear victory for Prussia, which secured some 35,000 square kilometres (14,000 sq mi) of new territory and around a million new subjects,[60] greatly enhancing its resources and prestige.

However, by twice making a separate peace while the War of the Austrian Succession raged on, Frederick abandoned his erstwhile allies in the League of Nymphenburg and earned a reputation for diplomatic unreliability and double-dealing.

[72][73] In the territorial settlement that ended the war, Prussia gained control of extensive new lands in Glatz and Silesia,[67] a populous and densely industrialised region that would contribute substantial manpower and taxes to the Prussian state.

[74][75] The small kingdom's unexpected victory over the Habsburg monarchy set it apart from German rivals such as Bavaria and Saxony, marking the beginning of Prussia's rise toward the status of a European great power.

The western invaders were driven back up the Danube Valley in early 1742,[83] and Saxony withdrew its forces from Bohemia after the Treaty of Berlin, making peace with Austria near the end of the year.

[84] By mid-1743, Austria would recover control of Bohemia, drive the French back across the Rhine into Alsace, and occupy Bavaria, exiling Emperor Charles VII to Frankfurt.