From the late 14th century, the city states of northern Italy were engaged in near continuous warfare triggered by the expansionism of the Visconti dynasty in Milan. Pitted against Milan was Florence, but, as the conflict evolved, Venice exploited the disruption by systematically extending its territories westward, initially as the ally of Florence. When Cosimo de Medici seized power in Florence (1434), he responded to the threat posed by Venice by forging an alliance with Francesco Sforza, heir to the Viscontis in Milan. Cosimo went on to become principal architect of the Treaty of Lodi, which established peace between Venice and Milan. By the Treaty, Sforza rule in Milan was recognized, while Venice cemented its territorial gains. Further, the mutual self-defence Italian League of Venice, Milan and Florence was established, with the Papal States and Naples joining the following year. The League would survive until the French invasion of 1494.
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