Frederick William succeeded to the throne on 16 November 1797.
He also became, in personal union, the sovereign prince of the Principality of Neuchâtel (1797–1806 and again 1813–1840).
At once, the new King showed that he was earnest of his good intentions by cutting down the expenses of the royal establishment, dismissing his father's ministers, and reforming the most oppressive abuses of the late reign.
He had the Hohenzollern determination to retain personal power but not the Hohenzollern genius for using it.
Too distrustful to delegate responsibility to his ministers, he greatly reduced the effectiveness of his reign since he was forced to assume the roles he did not delegate.
This is a main factor of his inconsistent rule.

Disgusted with the moral debauchery of his father's court (in both political intrigues and sexual affairs), Frederick William's first, and most successful early endeavor was to restore the moral legitimacy to his dynasty.
The eagerness to restore dignity to his family went so far that it nearly caused sculptor Johann Gottfried Schadow to cancel the expensive and lavish Prinzessinnengruppe project, which was commissioned by the previous monarch Frederick William II.
He was quoted as saying the following,  which demonstrated his sense of duty and peculiar manner of speech:
Every civil servant has a dual obligation: to the sovereign and to the country.
It can occur that the two are not compatible; then, the duty to the country is higher.

At first Frederick William and his advisors attempted to pursue a policy of neutrality in the Napoleonic Wars.
Although they succeeded in keeping out of the Third Coalition in 1805, eventually Frederick William was swayed by the attitude of the queen, who led Prussia's pro-war party, and entered into war in October 1806.
On 14 October 1806, at the Battle of Jena-Auerstädt, the French effectively decimated the effectiveness and functionality of the Prussian army led by Frederick William, and the Prussian army collapsed entirely soon after.
Napoleon occupied Berlin in late October.
The royal family fled to Memel, East Prussia, where they fell on the mercy of Emperor Alexander I of Russia.

Alexander, too, suffered defeat at the hands of the French, and at Tilsit on the Niemen France made peace with Russia and Prussia.
Napoleon dealt with Prussia very harshly, despite the pregnant Queen's personal interview with the French emperor which was believed would soften the blow of defeat.
Instead, Napoleon took much less mercy on the Prussians than what was expected.
Prussia lost many of its Polish territories, as well as all territory west of the Elbe, and had to finance a large indemnity and to pay for French troops to occupy key strong points within the Kingdom.

Although the ineffectual King himself seemed resigned to Prussia's fate, various reforming ministers, such as Heinrich Friedrich Karl, baron von und zum Stein, Prince Karl August von Hardenberg, Gerhard Johann David von Scharnhorst, and Count August von Gneisenau, set about reforming Prussia's administration and military, with the encouragement of Queen Luise (who died, greatly mourned, in 1810).

In 1813, following Napoleon's defeat in Russia, Frederick William turned against France and signed an alliance with Russia at Kalisz, although he had to flee Berlin, still under French occupation.
Prussian troops played a key part in the victories of the allies in 1813 and 1814, and the King himself travelled with the main army of Karl Philipp Fürst zu Schwarzenberg, along with Alexander of Russia and Francis of Austria.

At the Congress of Vienna, Frederick William's ministers succeeded in securing important territorial increases for Prussia, although they failed to obtain the annexation of all of Saxony, as they had wished.
Following the war, Frederick William turned towards political reaction, abandoning the promises he had made in 1813 to provide Prussia with a constitution.
Frederick William succeeded to the throne on 16 November 1797. He also became, in personal union, the sovereign prince of the Principality of Neuchâtel (1797–1806 and again 1813–1840). At once, the new King showed that he was earnest of his good intentions by cutting down the expenses of the royal establishment, dismissing his father's ministers, and reforming the most oppressive abuses of the late reign. He had the Hohenzollern determination to retain personal power but not the Hohenzollern genius for using it. Too distrustful to delegate responsibility to his ministers, he greatly reduced the effectiveness of his reign since he was forced to assume the roles he did not delegate. This is a main factor of his inconsistent rule.
Disgusted with the moral debauchery of his father's court (in both political intrigues and sexual affairs), Frederick William's first, and most successful early endeavor was to restore the moral legitimacy to his dynasty. The eagerness to restore dignity to his family went so far that it nearly caused sculptor Johann Gottfried Schadow to cancel the expensive and lavish Prinzessinnengruppe project, which was commissioned by the previous monarch Frederick William II. He was quoted as saying the following,  which demonstrated his sense of duty and peculiar manner of speech:
Every civil servant has a dual obligation: to the sovereign and to the country. It can occur that the two are not compatible; then, the duty to the country is higher.
At first Frederick William and his advisors attempted to pursue a policy of neutrality in the Napoleonic Wars. Although they succeeded in keeping out of the Third Coalition in 1805, eventually Frederick William was swayed by the attitude of the queen, who led Prussia's pro-war party, and entered into war in October 1806. On 14 October 1806, at the Battle of Jena-Auerstädt, the French effectively decimated the effectiveness and functionality of the Prussian army led by Frederick William, and the Prussian army collapsed entirely soon after. Napoleon occupied Berlin in late October. The royal family fled to Memel, East Prussia, where they fell on the mercy of Emperor Alexander I of Russia.
Alexander, too, suffered defeat at the hands of the French, and at Tilsit on the Niemen France made peace with Russia and Prussia. Napoleon dealt with Prussia very harshly, despite the pregnant Queen's personal interview with the French emperor which was believed would soften the blow of defeat. Instead, Napoleon took much less mercy on the Prussians than what was expected. Prussia lost many of its Polish territories, as well as all territory west of the Elbe, and had to finance a large indemnity and to pay for French troops to occupy key strong points within the Kingdom.
Although the ineffectual King himself seemed resigned to Prussia's fate, various reforming ministers, such as Heinrich Friedrich Karl, baron von und zum Stein, Prince Karl August von Hardenberg, Gerhard Johann David von Scharnhorst, and Count August von Gneisenau, set about reforming Prussia's administration and military, with the encouragement of Queen Luise (who died, greatly mourned, in 1810).
In 1813, following Napoleon's defeat in Russia, Frederick William turned against France and signed an alliance with Russia at Kalisz, although he had to flee Berlin, still under French occupation. Prussian troops played a key part in the victories of the allies in 1813 and 1814, and the King himself travelled with the main army of Karl Philipp Fürst zu Schwarzenberg, along with Alexander of Russia and Francis of Austria.
At the Congress of Vienna, Frederick William's ministers succeeded in securing important territorial increases for Prussia, although they failed to obtain the annexation of all of Saxony, as they had wished. Following the war, Frederick William turned towards political reaction, abandoning the promises he had made in 1813 to provide Prussia with a constitution.
Frederick William III of Prussia