The Monarchists had already assumed a position of power in Italy when the republican movement was initiated by Mazzini. This is particularly important when talking about its unification because they possessed the authority to legitimately influence important decisions. It was because Cavour decided to aim for economic development and a liberal approach at governance therefore that he could incline the opinion of Lucca, Tuscany, Modena, Parma and Romagna towards uniting themselves with Piedmont.
The system of monarchy was popular in Europe throughout the 19th century, so there weren’t a lot of countries that had an objection to it in Italy. Therefore, the monarchists also faced much less repression. It was also because the monarchs opted to win over powerful entities like the Catholic Church and France. This gave them an added edge in terms of fighting Austria, which was a country largely in favor of a divided Italy. It was as a result of the alliance between Cavour and Napoleon III that the battle of Magenta and Solferino were fought and Lombardy was won back.
The efforts made by different republicans weren’t entirely negligible. Mazzini managed to influence many people with his ideas including Garibaldi. He was responsible for the creation of Young Italy. However, the society’s attempts to penetrate the Sardianian army, invade Savoy and provoke a revolution in Genoa ended in a disaster. Also, Garibaldi’s expedition, more popularly known as the advent of ‘The Thousand’ yielded significant results. It was because of this that King Francis II was forced to abandon Naples.
After Garibaldi had set sail, however, Cavour realized that he was succeeding and there was a high chance that he would aim at taking over Rome. This would cause problems in two ways, first because Europe would intervene and second because it would completely destroy relations Italy’s relations with France, which was the occupying force in Rome. So Cavour assembled his army and took over the Papal States all under the pretext of stopping Garibaldi. During this time it seems as though Cavour still did not intend on uniting Italy but rather preserving the relationships it had attained over time within Europe.
It was because Cavour took over this part and Garibaldi took over the Southern side that in 1861 Italy could finally present itself as a country with the exception of Venetia and Rome which it would gain later. This event also gathered an immense amount of support from landowners and peasants within the two Sicilies, which were annexed after a plebiscite was held. Before any attempt could be made at reclaiming the two states that Italy was still missing Cavour passed away. It was now up to the republicans to attain the aforementioned states.
Venetia was handed over to Italy by France after a battle against Austria. Even though Mazzini and Garibaldi both tried to take over Rome from Napoleon II after he refused to honor his commitment and give it up voluntarily, they failed to do so. It was only as a result of the Franco-Prussian war in 1870 that France was forced to withdraw its army from Rome and it was annexed to Italy. Although the monarchists did possess a significant amount of power, it was Mazzini who acted as an initiator of change and Garibaldi who acted on it militarily.
However, in terms of who contributed to the unification the most, it has to be the Monarchists. They were inevitably the ones who had the ability to alter state policy and empower the army. The former led to the winning over of support in other states and by other countries. The latter allowed for Austria to be threatened to the point where they felt the need to retreat. It was also this factor that helped Garibaldi in his expedition which would otherwise have failed.