Throughout the fourteenth century, Florence was a tenacious opponent of the expansionist policies of the Visconti, the lords and then dukes of Milan who aimed at establishing a solid and large state in Northern Italy. Between the late 1390s and the early 1400s, Gian Galeazzo Visconti extended his dominions and influence to Bologna, Perugia and Tuscany itself, thereby posing a serious challenge to the very position held by Florence in Central Italy. His sudden death, in 1402, and the almost immediate disintegration of his powerful duchy – which was soon reduced to a conglomerate of cities and territories ruled by local lords – seemed to liberate Florence and other Italian states from such a threat. In 1412, however, his younger son, Filippo Maria, became duke. Filippo engaged in a gradual and skilful restoration of the dominions that had been lost in the previous decade. First, he neutralised the hostility of the local lords around Milan; then, after consolidating his power, he ridded himself of them in various ways and began to regain the other dominions. While doing this, the young Duke needed to make sure that the other Italian powers, above all Venice and Florence, would not interfere with his designs. He kept Venice quiet by giving up his claims on Verona and Vicenza, seized by the Venetians after his father's death; as for the Florentines, whose attitude was instrumental to the recovery of Genoa, he offered them a treaty of peace and non-interference in their respective spheres of influence – a reciprocal guarantee that his ambassadors presented as a manifestation of his good faith and desire to break with his family's expansionist tradition.

The debate that follows is about this offer, which was indeed accepted by the Florentines (the treaty was signed on 8 February 1420). To Guicciardini, the decision reflected in particular the desire not to antagonise the popular party, whose members suspected that those who spoke against Filippo's peace plan stood to gain some personal advan-tage from war. Thus, the supporters of the peace became more vocal, those who held a different view turned more reserved, and those in between embraced the prevailing opinion, ‘whose good was evident and whose evil was so hidden that only a perspicacious eye could see it’.