Without the aid of Florence and Cosimo de’ Medici, he would not have attained his ends. Cosimo had recognised his ability in the war with Visconti, and made a close alliance with him. In order to retain him in his service, when Filippo Maria offered him as a bait the hand of his daughter, Cosimo had gone in 1438 to Venice, in order to obtain more favourable conditions for him from the Republic, friendly to himself, in which, however, he failed. During the distress of Sforza on the frontiers, he had supported him as much as he could. His son Piero was present at Sforza’s marriage. Now it was necessary to choose between Sforza and Venice, for there was only one alternative; either the _condottiere_ would make himself Duke of Milan, or the Republic of San Marco would extend its rule over all Lombardy. In Florence several voices declared in favour of the old ally on the Adriatic, who, however she might seek her own advantage with unscrupulous zeal, had yet ever been faithful at critical moments. Cosimo de’ Medici gave the casting-vote in Sforza’s favour. Perhaps it was hard to think of his old personal connections and obligations, but political expediency gained the day. Without Florentine money, Sforza would never have been able to maintain the double contest—on the one side against Milan, which he blockaded and starved out; and on the other against the Venetians, who sought to relieve it, and whom he repulsed. And when, on March 25, 1450, he made his entry into the city which proclaimed him ruler, he was obliged to maintain himself with Florentine money till he had established his position and re-organised the State. A Florentine embassy went to congratulate him—Piero de’ Medici, Neri Capponi, Luca Pitti, Diotisalvi Neroni. The Venetians were exceedingly irritated, as was natural. They judged rightly that the Sforza owed his success essentially to the favour of their former friends. Their indignation became fiercer when Florence entered into negociations (June 29) with King Alfonso, with whom they were still at war. Common animosity to Florence and Sforza drew Venice and the king nearer to one another, and at the end of 1451 an alliance, offensive and defensive, was concluded against them, which Siena, Savoy, and Montferrat joined. It was at first directed against the Duke of Milan; the Florentines had the choice of joining it, for form’s sake. But when they replied that, as peace prevailed in Italy, new alliances were not necessary, the Venetians banished all the Florentine merchants from their territories, refused a hearing to Otto Niccolini, who was entrusted with an embassy, and persuaded the king to adopt like measures. On May 16, 1452, the Republic and, four weeks later, King Alfonso declared war, which the Emperor Frederick III., then in Italy, and Pope Nicholas V., successor to Eugenius IV. since 1447, in vain endeavoured to prevent.