Duke Filippo Maria Visconti died in Milan without a legitimate male heir, ending the Visconti male line. His death created a power vacuum and opened competing claims and interventions by neighboring powers. This moment set the stage for Milan’s brief republican experiment and a wider war over the duchy.
After the duke’s death, leading Milanese figures proclaimed a republic, later known as the (Golden) Ambrosian Republic. It was governed by a small ruling group often described as “captains and defenders of liberty,” attempting to preserve autonomy against outside claimants. The republic immediately faced war pressure, especially from Venice.
To defend the former duchy’s territory, the republic mobilized its citizens and relied heavily on Francesco Sforza, a leading condottiero (mercenary commander) and the late duke’s son-in-law. Using hired commanders helped Milan field armies quickly but also created a risk: the commander’s interests could diverge from the city’s. This decision tied the republic’s survival to Sforza’s loyalty.
Sforza secured control of Pavia, a key city near Milan, strengthening his strategic position in the succession struggle. Holding major towns increased his bargaining power with the republic and with rival states. It also fed suspicions in Milan that its “protector” might become its main threat.
After a long siege, Piacenza was taken back under Milanese/Sforza control, but the aftermath included major violence and looting described in later accounts. Events like this hardened political divisions inside Milan about whether Sforza was safeguarding the republic or building a personal power base. The republic’s internal unity weakened as the external war continued.
By early 1448, Milan’s governing councils changed composition, reflecting factional rivalry and public pressure. At the same time, Milan explored peace talks with Venice, showing how military strain pushed leaders toward compromise. These political swings made consistent strategy difficult and increased the chances of a break with Sforza.
Sforza led the Ambrosian Republic’s forces to victory over the Venetian army at Caravaggio. The battle was a major turning point: it demonstrated Sforza’s military value while also raising his prestige and independence. After this, the question became less whether Sforza could win battles and more who would control Milan’s future.
Soon after Caravaggio, Sforza and Venice reached a secret agreement at Rivoltella. The deal aimed to help Sforza take Milan in exchange for territorial concessions to Venice (including Bergamo and Brescia). This marked a clear shift: Sforza moved from being the republic’s commander to acting as an independent contender for the duchy.
With Sforza increasingly seen as a threat, Milan sought outside help and received a force of French mercenaries sent by King Charles VII. The republic also pursued additional alliances, trying to counterbalance Sforza’s growing strength. These measures show how the republic’s survival depended on shifting coalitions rather than stable institutions.
Despite earlier promises, Venice later broke with Sforza during the campaign around Milan, reshuffling the war’s alliances again. Sforza’s forces tightened pressure on Milan, and the city struggled with supply problems and political exhaustion. The republic’s position became increasingly fragile as the war dragged on.
In early 1450, Milan’s population, strained by hunger and instability, rebelled against the republic’s leaders. The city’s gates were opened to Sforza, effectively ending the Ambrosian Republic as a functioning regime. This was the decisive internal collapse that enabled the Sforza restoration.
Sforza entered Milan and was formally confirmed as duke, replacing the republic with dynastic rule. His accession began the Sforza line in Milan and re-centered the city-state around a princely court rather than republican councils. The “restoration” also connected Milan’s future to wider Italian power politics and treaty-making.
The Peace of Lodi ended the broader Milanese succession conflict between Milan and Venice and recognized Sforza’s rule. It helped create a more stable balance among major Italian states for decades, reducing the immediate risk of another succession war. As an outcome, the short Ambrosian Republic became a cautionary example of how fragile city-state republican rule could be under intense military pressure.
Ambrosian Republic and the Sforza Restoration (1447–1450)