Complex sentence: When the larger military operations turned against the Piedmontese, that retreated, Brescia was left to its own resources, but managed to resist recapture by the Austrian army for ten days of bloody and obstinate street fighting that are now celebrated as the Ten Days of Brescia.
Split into simpler sentences: When the larger military operations turned against the Piedmontese, forcing them to retreat, Brescia was left to its own resources. Still, the citizens managed to resist recapture by the Austrian army for ten days of bloody and obstinate street fighting that are now celebrated as the Ten Days of Brescia.