In August 1313 the German throne had again become vacant, and Louis was chosen at Frankfort on the 20th of October 1314 by a majority of the electors, and his coronation followed at Aix-la-Chapelle on the 25th of November. A minority of princes had, however, supported Frederick of Austria; and a war followed between the rivals, during which Louis was supported by the cities and the districts of the middle and lower Rhine. His embarrassments were complicated by a renewal of the dispute with his brother; but when this had been disposed of in 1317 by Rudolph's renunciation of his claims on upper Bavaria and the Palatinate in consideration of a yearly subsidy, Louis was able to give undivided attention to the war with Frederick, and obtained several fresh allies. On the 28th of September 1322 a battle was fought at Mühldorf, which ended in a complete victory for Louis, owing mainly to the timely aid of Frederick IV. of Hohenzollern, burgrave of Nüremburg. Frederick of Austria was taken prisoner, but the struggle was continued by his brother Leopold until the latter's death in 1326. Attempts to enable the two kings to rule Germany jointly failed, and about 1326 Frederick returned to Austria, leaving Louis in undisputed possession of the country. Before this conclusion, however, a new enemy had taken the field. Supported by Philip V. of France in his desire to free Italy entirely from German influence, Pope John XXII. refused to recognize either Frederick or Louis, and asserted his own right to administer the empire during a vacancy. After the battle of Mühldorf Louis sent Berthold of Neifen, count of Marstetten, into Italy with an army, which soon compelled the papal troops to raise the siege at Milan. The pope threatened Louis with excommunication unless he resigned his kingdom within three months. The king thereupon appealed to a general council, and was placed under the papal ban on the 23rd of March 1324, a sentence which he answered by publishing his charges against the pope. In the contest Louis was helped by the Minorites, who were upholding against John the principal of clerical poverty, and by the writings of Marsilius of Padua (who dedicated to Louis his _Defensor pacis_), William of Occam, John of Jandun and others. Taking the offensive, Louis met his Ghibelline supporters at Trent and reached Italy in March 1327; and in May he received the Lombard crown at Milan. Although the pope renewed his fulminations Louis compelled Pisa to surrender, and was hailed with great rejoicing in Rome. On the 17th of January 1328 he was crowned emperor in St Peter's by Sciarra Colonna, a Roman noble; and he answered the continued attacks of Pope John by pronouncing his deposition, and proclaiming Peter of Corvara pope as Nicholas V. He then undertook an expedition against John's ally, Robert, king of Naples, but, disunion among his troops and scarcity of money and provisions, drove him again to Rome, where, finding that his exactions had diminished his