The reign of the next landgrave, William IX. (1785-1821), was an important epoch in the history of Hesse-Cassel. Ascending the throne in 1785, he took part in the war against France a few years later, but in 1795 peace was arranged by the treaty of Basel. For the loss in 1801 of his possessions on the left bank of the Rhine he was in 1803 compensated by some of the former French territory round Mainz, and at the same time was raised to the dignity of Elector (_Kurfurst_) as William I. In 1806 he made a treaty of neutrality with Napoleon, but after the battle of Jena the latter, suspecting William's designs, occupied his country, and expelled him. Hesse-Cassel was then added to Jerome Bonaparte's new kingdom of Westphalia; but after the battle of Leipzig in 1813 the French were driven out and on the 21st of November the elector returned in triumph to his capital. A treaty concluded by him with the Allies (Dec. 2) stipulated that he was to receive back all his former territories, or their equivalent, and at the same time to restore the ancient constitution of his country. This treaty, so far as the territories were concerned, was carried out by the powers at the congress of Vienna. They refused, however, the elector's request to be recognized as "King of the Chatti" (_Konig der Katten_), a request which was again rejected at the conference of Aix-la-Chapelle (1818). He therefore retained the now meaningless title of elector, with the predicate of "royal highness." The elector had signalized his restoration by abolishing with a stroke of the pen all the reforms introduced under the French regime, repudiating the Westphalian debt and declaring null and void the sale of the crown domains. Everything was set back to its condition on the 1st of November 1806; even the officials had to descend to their former rank, and the army to revert to the old uniforms and powdered pigtails. The estates, indeed, were summoned in March 1815, but the attempt to devise a constitution broke down; their appeal to the federal diet at Frankfort to call the elector to order in the matter of the debt and the domains came to nothing owing to the intervention of Metternich; and in May 1816 they were dissolved, never to meet again. William I. died on the 27th of February 1821, and was succeeded by his son, William II. Under him the constitutional crisis in Hesse-Cassel came to a head. He was arbitrary and avaricious like his father, and moreover shocked public sentiment by his treatment of his wife, a popular Prussian princess, and his relations with his mistress, one Emilie Ortlopp, created countess of Reichenbach, whom he loaded with wealth. The July revolution in Paris gave the signal for disturbances; the elector was forced to summon the estates; and on the 5th of January 1831 a constitution on the ordinary Liberal basis was signed. The elector now retired to Hanau, appointed his son Frederick William regent, and took no further part in public affairs.