Why did Cavour fear Garibaldi’s success in southern Italy?

Count Cavour’s apprehension regarding Giuseppe Garibaldi’s success in southern Italy stemmed from several political and strategic concerns:

• Risk of French Intervention: Garibaldi intended to march on Rome to complete Italian unification. Because Rome was defended by a French garrison, Cavour feared that an attack on the city would provoke a hostile intervention by France, jeopardizing the progress already made.12
• Ideological Rivalry: Cavour feared that the Risorgimento was shifting from a state-led project into a popular, radical movement. He was concerned that Garibaldi’s radical followers, including republicans and supporters of Giuseppe Mazzini, might influence Garibaldi to abandon the monarchical cause in favor of a republic.312
• Political and Military Preeminence: Garibaldi had become a popular hero, arguably more so than the king himself. Cavour sought to ensure that Piedmont maintained leadership over the unification process, while the regular Piedmontese army was deeply jealous of Garibaldi’s military victories and determined to prevent him from achieving further success.12

To mitigate these risks, Cavour took the initiative to invade the Papal States, effectively checking Garibaldi’s momentum and ensuring the south was annexed under the authority of Victor Emmanuel II.31