Why were Rome and Venetia not initially part of the unified Kingdom of Italy?

When the Kingdom of Italy was proclaimed in 1861, Venetia and Rome remained outside the new nation due to the influence and military presence of foreign powers.1

• Venetia: This territory remained under Austrian rule following the political shifts of the early 19th century. It was not incorporated into the Kingdom of Italy until 1866, following Italy's alliance with Prussia during the war against Austria.23
• Rome: The city and its surrounding region remained separate because they were protected by French troops, who were stationed there to safeguard the pope's temporal power. The existence of the Papal States was a significant obstacle to unification, as foreign intervention protected papal independence. Rome was finally annexed in 1870, after the French garrison withdrew during the Franco-Prussian War, allowing Italian troops to enter the city and eventually establish it as the capital.143