Leo found the war renewed in Northern Italy. Louis XII. sent a fresh army, under La Trimouille, to invade the duchy of Milan. The Swim auxiliaries of Duke Maximilian Sforza defeated La Trimouille at Novara, and the French were driven out of Italy. The Venetians however had allied themselves with Louis XII., and Leo cent Bembo to Venice to endeavour to break the alliance. Differences broke out between Leo and Alfonso d'Este, duke of Ferrara, who demanded the restoration of Reggio, taken from him by Julius IL, which Leo pro mised, but never performed ; on the contrary, he purchased Modena of the Emperor Maximilian, disregarding the rights of the house of Este to that town. The l'ope held likewise Parma and Piacenza, and it appears that be intended to form out of these a territory for his brother Giuliano, and he made attempts to surprise Ferrara also with the same view. His predecessor, Julius, had in view the independence of all Italy, and he boldly led on the league for this purpose ; Leo had a narrower object,—his own aggrandisement and that of his family,— and he pursued it with a more cautious and crooked policy.
Leo re-opened the council of the Lateran, which bad begun under Julius IL, for the extinction of the schism produced by the council of Pisa, which had been convoked by Louie XII., in order to check the power of that pope, who was his enemy. Circumstances were now changed, and Louie XII. made his peace with Leo in 1514, renounced the council and acknowledged that of the Lateran. Louis XII. died in the following year, and his successor Francis I., among his other titles, assumed that of Duke of Milan, which was the signal of a new Italian war. The Venetians joined him, whilst the Emperor Maximilian, Ferdinand of Spain, Duke Sforza, and the Swiss, made a league to oppose the French. The Pope did not openly join the league, but he negociated with the Swiss by means of the cardinal of Sion, and paid them considerable sums to induce them to defend the north of Italy. The Swiss were posted near Susa, buteFrancie, led by old Trivulzio, passed the Alps by the Col de l'Argentier, entered the plains of Salozzo, and marched upon Pavia, whilst the Swiss hastened back to defend Milan. The battle of Marignano was fought on the 14th of September 1515. The Swiss made desperate efforts, and would probably have succeeded, had not Alviano with part of the Venetian troops appeared suddenly with cries of " Viva San Marco," which dispirited the Swiss, who believed that the whole Venetian army was coming to the assistance of the French. The result was the retreat of the Swiss, and the entrance of the French into Milan, who took posses Bien of the Duchy. Leo now made proposals of alliance to Fraueia, who eagerly listened to them, and they had a conference at Bologna in December 1515, in which a concordat was agreed upon, regulating the appointment to the sees and livings in the French kingdom, which concordat remained in force till the French Revolution. A marriage was also agreed upon between Lorenzo, the pope's nephew, and Madeleine de Boulogne, niece of Francis de Bourbon, duke of Vendome, from which marriage Catherine de Medici, afterwards Queen of France, was born.
In 1516 Leo, under some frivolous pretences, deprived Della Rovere, the nephew of Julius II., of his duchy of Urbino, Pesaro, and Sinis gaglia, which he gave to his nephew Lorenzo de' Medici. Soon after wards a conspiracy to murder the pope was discovered at Rome, and Cardinal Petrucci, who was at the head of it, was hanged. In 1517 the council of the Lateran was finally closed, and in the same year Leo authorised the sale of indulgences iu Germany, which was the immediate cause of the Reformation. (Luna%) For some years after however Leo took little notice of the progress of Luther's opinions in Germany ; and indeed to the end of his life Leo's mind appears to have been much more concerned with what occurred around him in Italy than with the remote controversy carried on in Saxouy, the consequences of which he probably did not foresee.
In 1518 a league of five years was proclaimed by Leo among the Christian princes to oppose the advance of the Turks, who were tbreateuing Italy. For this purpose the pope gave to the Christian princes the disposal of part of the revenues of the clergy, which they readily appropriated to themselves, without doing anything against the Turks.
Gian Paolo Baglione of Perugia, a celebrated condottiero, bad seized upon the government of hie native town. Lee cited him to appear at Rome, with promises however of safety for his person. Upon his arrival Baglione was arrested, put to the torture, made to confess many crimes, and at last beheaded. Perugia was then annexed to the Papal State, as well as the duchy of Urbino after the death of Lorenzo de' Medici, who left no male issue.
The alliance of Leo with Francis I. was a hollow one, each party mistrusting the other. At last Leo, thinking an alliance with the young monarch of Spain and Emperor of Germany was likely to be much more advantageous to him, concluded a secret treaty, offensive and defensive, with Charles V., on the 8th of July 1521, by which it was stipulated that the- duchy of Milan was to be taken from the French and given to Francesco Maria Sforza, and Parma and Piacenza to be restored to the pope. Leo subsidised a body of Swiss, and Prospero Colonna with the Spaniards from Naples joined the Papal forces at Bologna, crossed the Po at Casalmaggiore, joined the Swies, and drove the French governor Lantrec out of Milan. In a short time the duchy of Milan was once more clear of the French, and reetored to the dominion of Sforza. Parma and Piaceuza were again occupied by the Papal troope. Leo at the same time declared Alfonso d'Eete a rebel to the Holy See for having sided with the French, whilst the duke on his part complained of the bad faith of the pope in keeping possession of Modena and Reggio. The news of the taking of Milan was celebrated at Rome with public rejoicings, but in the midst of all this Leo fell ill, on the 25th of November, and died on the 1st of December 1521, being forty-six years of age, not without suspicion of poison, though eome have maintained that he died a natural death.