Frederick William III., eldest son and successor of the preceding, born Aug. 3, 1770, died June 7, 1840. Educated with care by his virtuous mother, Louisa of Hesse-Darmstadt, he had ample opportunity of comparing, at the courts of Frederick the Great and of his father, the opposite influence of royal virtues and vices upon the affairs of his state; and he early contracted the love of order, discipline, economy, and labor, which in after time contributed no little to the prosperity of his people. He accompanied his father to the conference of Pilnitz, and to the army of the first coalition against France, and in 1793 married the beautiful and accomplished princess Louisa of Meck-lenburg-Strelitz, the most popular queen of Prussia. After his accession (Nov. 16, 1797) the court and the administration were purged of the creatures and abuses of the preceding reign. The unpopular edicts restricting the press and the freedom of religious instruction were abrogated, and economy and order restored. In his foreign policy the young king maintained the neutrality imposed by the treaty of Basel, the temporary stipulations of which were made definitive by the treaty of Luneville (1801). For its cessions on the left bank of the Rhine, Prussia soon after received ample compensations in small territories deprived of their independence as members of the empire by decree of the Germanic diet.

Satisfied with his acquisitions and political influence in the north of Germany, Frederick William refused to join the third coalition against France which was formed by England, Russia, and Austria. But when the French armies had infringed the neutrality of the Prussian territories, he secretly allied himself with Alexander of Russia, during a sudden visit of the latter at Berlin. Hesitation, however, spoiled the effect of this alliance, and the battle of Austerlitz was followed by a new treaty with Napoleon (December, 1805). Ceding Anspach, Cleves, and Neufchatel, Prussia received Hanover from the conqueror. The consequence of this exchange was what Napoleon wanted, a declaration of war by England against Prussia. The latter was also embroiled with Sweden. Having made peace with these enemies, Frederick William made peremptory demands on Napoleon in behalf of the neutrality of his state and its allies in northern Germany. Napoleon answered with prompt hostilities, and the battles of Jena and Auerstadt were both fought on Oct. 14, 1806. The powerful Prussian army was broken, Berlin was occupied by the enemy, and the fortresses surrendered at the first summons. The aid of Alexander was of little avail.

After a winter campaign in Prussian Poland and the indecisive battles of Pultusk (Dec. 26) and Eylau (Feb. 7-8, 1807), Napoleon conquered peace by the battle of Friedland, won on the anniversary of Marengo (June 14). The treaty of Tilsit (July) sacrificed one half of Prussia, parts of which were transformed into the duchy of Warsaw, and others attached to the kingdom of Westphalia. The other half remained for years in the hands of the conqueror, and was treated as a subdued province. The treaty further provided for the reduction of the Prussian army to 40,000 men, and the payment of an indemnity of 146,000,000 francs to France. French troops were to occupy Berlin and other important Prussian fortresses till the payment of the debt. The king, who paid a visit with the queen to Alexander, could not return to his capital before 1809. But this gloomy period became one of the most successful in the history of the state, by a series of salutary and energetic reforms, undertaken and executed particularly under the celebrated ministers Stein and Hardenberg. Serfdom was abolished, the towns obtained some independence in the management of their affairs, the royal domains were sold, convents and ecclesiastical foundations were converted into state property, public instruction was organized, and' the new university of Berlin founded.

The new system of military organization of Prussia had also its origin in that period. In July, 1810, the king lost his wife. In 1812 he was compelled to aid Napoleon with an army against Russia. Forming the left of the great French army of invasion, it was saved on the retreat by a special arrangement between its commander, York, and Diebitsch.' Frederick in January, 1813, transferred his residence to Breslau, where he was visited in March by the emperor Alexander, and the treaty of Kalisz, which had been concluded the preceding month between Russia and Prussia, was made public. He now issued a proclamation, which was answered by a general rising of the nation against France. The capital alone is said to have contributed 10,000 men. Prudent measures had been adopted in secret to prepare for the struggle. The young men, meeting privately, had been drilled in the use of arms in small detachments. Thus the power of the people answered to their will. The militia having been summoned, war against France was declared on March 17. The situation had its dangers. The French still held the fortresses of Prussia and Poland; their army in the dominions of the king still amounted to 60,000. But Napoleon's hour of success had passed.

The continual desertion of his allies served to strengthen the phalanx of the coalition after every defeat of his armies. His enormous new levies were not sufficient to cover the extraordinary losses, and to face so many enemies. The Prussians fought bravely in various engagements in 1813 and 1814 (see Blu-cher), and the king often gave proofs of personal activity and courage. He entered Paris with his allies, accompanied Alexander on his visit to England, made a triumphal entry into his capital in August, 1814, and repaired to the congress of Vienna. The stipulations of this congress conferred on Prussia greater power than it possessed before the wars, enlarging it particularly with parts of Saxony, one of the last allies of Napoleon. The sudden return of the captive of Elba called the Prussians again to arms, and Blucher, after his previous defeat, appeared at Waterloo in time to finish the great struggle. The last 25 years of the reign of Frederick William form a period of undisturbed peace and prosperity for Prussia. Closely allied with the czar Alexander, and afterward with Nicholas, the king pursued a policy of strict conservatism. Much was done for internal improvements, little for political reform.

He, however, formed the great German commercial league, the Zollverein. Revolutionary agitations, wherever they manifested themselves, were suppressed with severity. The last years of his reign were agitated by a strife with the Roman Catholic clergy. The eldest of his four sons succeeded him. One of his daughters was married to the emperor Nicholas. In 1824 he had formed a morganatic marriage with the countess Augusta of Harrach, whom he made princess of Liegnitz. She died in Hamburg, June 6, 1873, aged 72.