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Why did the Roman Republic of 1849 collapse?

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Italian revolutionary Giuseppe Mazzini — Giuseppe Mazzini Giuseppe Mazzini, detail of an oil painting by Luigi Zuccoli, 1865; in the Museo del Risorgimento, Milan.

The Roman Republic of 1849 collapsed primarily due to military intervention by French forces, who were prompted to act after Pope Pius IX appealed to Catholic powers to restore his authority following his ousting from the Papal States.12

Louis-Napoleon (Napoleon III) intervened to appease French Catholics and preempt an Austrian invasion of the region. Although the Roman garrison, led by Giuseppe Garibaldi, initially repelled the French in April 1849, the French returned with a significantly larger force of 30,000 troops equipped with heavy artillery.1

The siege began in earnest on June 1, 1849. The republic’s defenses were compromised when the crucial position at Villa Pamphili was overwhelmed, allowing French guns to dominate the city. Despite heroic resistance, the republic was eventually crushed, leading to the restoration of papal authority in July 1849 and the departure of Giuseppe Mazzini, who had served as a triumvir and the effective head of the government.12