The remainder of Ludwig's reign might have been untroubled, but for a family difficulty. The Empress Judith demanded that her son, Karl, should also have a kingdom, like his three step-brothers. An Imperial Diet was therefore called together at Worms, in 829, and, in spite of fierce opposition, a new kingdom was formed out of parts of Burgundy, Switzerland and Suabia. The three sons, Lothar, Pippin and Ludwig, acquiesced at first; but when a Spanish count, Bernard, was appointed regent during Karl's minority, the two former began secretly to conspire against their father. They took him captive in France, and endeavored, but in vain, to force him to retire into a monastery. The sympathies of the people were with him, and by their help he was able, the following year, to regain his authority, and force his sons to submit. [Sidenote: 833.] Ludwig, however, manifested his preference for his last son, Karl, so openly that in 833 his three other sons united against him, and a war ensued which lasted nearly five years. Finally, when the two armies stood face to face, on a plain near Colmar, in Alsatia, and a bloody battle between father and sons seemed imminent, the Pope, Gregory IV., suddenly made his appearance. He offered his services as a mediator, went to and fro, and at last treacherously carried all the Emperor's chief supporters over to the camp of the sons. Ludwig, then sixty years old and broken in strength and spirit, was forced to surrender. The people gave the name of "The Field of Lies" to the scene of this event. The old Emperor was compelled by his sons to give up his sword, to appear as a penitent in Church, and to undergo such other degradations, that the sympathies of the people were again aroused in his favor. They rallied to his support from all sides: his authority was restored, Lothar, the leader of the rebellion, fled to Italy, Pippin had died shortly before, and Ludwig proffered his submission. The old man now had a prospect of quiet; but the machinations of the Empress Judith on behalf of her son, Karl, disturbed his last years. His son Ludwig was marching against him for the second time, when he died, in 840, on an island in the Rhine, near Ingelheim.