The elector had signalized his restoration by abolishing with a stroke of the pen all the reforms introduced under the French régime, 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 Ortlöpp, 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.
The regent, without his father's coarseness, had a full share of his arbitrary and avaricious temper. Constitutional restrictions were intolerable to him; and the consequent friction with the diet was aggravated when, in 1832, Hassenpflug (q.v.) was placed at the head of the administration. The whole efforts of the elector and his minister were directed to nullifying the constitutional control vested in the diet; and the Opposition was fought by manipulating the elections, packing the judicial bench, and a vexatious and petty persecution of political "suspects," and this policy continued after the retirement of Hassenpflug in 1837. The situation that resulted issued in the revolutionary year 1848 in a general manifestation of public discontent; and Frederick William, who had become elector on his father's death (November 20, 1847), was forced to dismiss his reactionary ministry and to agree to a comprehensive programme of democratic reform. This, however, was but short-lived. After the breakdown of the Frankfort National Parliament, Frederick William joined the Prussian Northern Union, and deputies from Hesse-Cassel were sent to the Erfurt parliament. But as Austria recovered strength, the elector's policy changed. On the 23rd of February 1850 Hassenpflug was again placed at the head of the administration and threw himself with renewed zeal into the struggle against the constitution and into opposition to Prussia. On the 2nd of September the diet was dissolved; the taxes were continued by electoral ordinance; and the country was placed under martial law. It was at once clear, however, that the elector could not depend on his officers or troops, who remained faithful to their oath to the constitution. Hassenpflug persuaded the elector to leave Cassel secretly with him, and on the 15th of October appealed for aid to the reconstituted federal diet, which willingly passed a decree of "intervention." On the 1st of November an Austrian and Bavarian force marched into the electorate.