Cavour became prime minister of Piedmont in 1852 and whilst he had not set out to unify Italy he was very much interested in extending the rule of Piedmont in northern and central Italy. First and foremost, Cavour was a Piedmontease nationalist who encouraged economic developments in the 1850’s and helped implement the modernisation of Piedmont such as the construction of a railway, improved infrastructure, a stabilized economy, raised money for possible wars and strengthened Sicily. This gave Piedmont the chance to rise up and eject Austrian power from Italy which was essential to a unified Italy. In this respect it would seem he made a significant contribution to Italian unification. However, this is too simplistic. Cavour wanted to create a northern Italian kingdom under Victor Emmanuel II. This was clearly the motivation behind the French alliance and subsequent war with Austria. Prime Minister Cavour persuaded Napoleon III of France to sign a secret treaty of alliance with Piedmont (at Plombieres), called the Plombieres agreement 1858, which allowed the French to intervene on the side of the Piedmontese once Cavour had provoked Austria into a war. Cavour was prepared to cede to France the territories of Nice and Savoy in order to gain French acceptance of Piedmonts annexation of central Italy, which demonstrates to us his actual lack of commitment to the idea of Italian unification. However, the war had encouraged Italians to rise up against the Austrians in northern Italy and to achieve independence for many of the other northern Italian states. Cavour stirred uprisings in the Pope's northernmost territories, which infuriated France but meant great things for the unification cause. These states accepted potential unification under the government of Piedmont thanks to Cavour's determination and also the help of the National society, who were encouraging voters in the Central Duchies to request annexation by Piedmont.
To achieve Italian unity, Cavour knew he would never be able to rely on a revolt from the people nor the secret societies that were very popular. Italian Unification would have to be achieved through fierce political combat to drive the Austrian Empire out, and then brutal war on the smaller powers of the Italian peninsula. To gain a foothold in the grand political arena of Europe, Cavour sent troops to Russia to participate in the Crimean War in 1854. Whereas Austria got no support from Russia because of its failure to support the Russians during the Crimean War. As a result this helped indirectly unify Italy due to Austria’s diplomatic isolation and having lost control of northern Italy, Austria was in no position to prevent Garibaldi’s invasion in the south.
Cavour did play a significant role in Italian unification but he wasn’t the sole reason for a unified Italy; there were several other crucial factors one being the role that Garibaldi played. Garibaldi was a passionate supporter of Italian unification. Heavily influenced by Mazzini, Garibaldi had been involved in several earlier revolutions in the Italian states. He hoped to take advantage of what Cavour has achieved in the north to complete the unification process.
Whilst Cavour was the politician/diplomat, Garibaldi was the military leader. A prominent member of Italian secret societies, he organized 1,150 Red Shirts into what was called "Garibaldi's Thousand." He invaded the Two Sicilies, and the government there collapsed around itself as thousands of citizens rallied behind Garibaldi. His conquests of Sicily and Naples were a worrying development for Cavour who was deeply suspicious of Garibaldi’s republican and democratic views. Garibaldi’s intervention in the south forced Cavour to complete the unification process. Cavour now took the view that if Italy was going to be unified it would be on Piedmont’s terms and by September 1860 Piedmont troops were occupying the Papal States. Garibaldi surrendered his conquests to Piedmont which allowed the northern and southern states of Italy to be united.
And by surrendering his southern conquests to Piedmont Garibaldi's influence, it seems to me, was small in the big scheme of things and although he was influenced by Mazzini, who played a great role in organising and initiating the transformation, there is reason to believe he just arrived at the end and picked up the spoils and glory that came with it. The Red-Shirts took Sicily and he hailed himself Dictator of the island.
It will not suffice to give all the credit for these revolutionary movements to Garibaldi, the soldier, however he played contributory role and without Garibaldi, Cavour’s significance would have been diminished.
Another contributing factor to the unification was Mazzini who had been the political idealist able to catalyse the national spirit of the Italian people into a viable force, being one of the first to introduce the practical possibility of unification. He was very much the propagandist of Italian unity, however post 1848-9, in the wake of revolutionary failure the Mazzinian ideas which to a degree had instigated the popular unrest of the early nineteenth century, had been proven impractical and unworkable. Indeed Piedmont was the most promising tool for unification, which explains the significance of Cavour's ambition, in that it provided the means with which others could achieve independence from foreign rule and unification. Garibaldi on the other hand complimented politics with military force and action capitalizing on Cavour's and the King's ignorance of situations in the South.
The last factor to consider is that of foreign intervention. The involvement of foreign powers was also contributory to Italian unification. France was important to Italy in 1859 under Napoleon III and the direct intervention of France was crucial to unification of Italy. France was looking to undermine Austria’s position in Italy which helped Piedmont to remove Austrian power from Lombardy and Venetia. Britain was sympathetic to the cause of Italian nationalism and the British navy also played a role in Garibaldi’s invasion of Sicily. Without support from Britain’s navy, ‘Garibaldi’s thousand’ may not have been able to conquered southern Italy thus making it impossible to unite north with south which would prevent any means of unification.
Cavour was initially motivated to make Piedmont grand, but I feel no unification would have been possible without the removal of Austrian power from the peninsula. Cavour’s negotiation of the Plombieres agreement was crucial in achieving this. His intervention in the south in 1860 insured that Italy was unified under the king of Piedmont. For these reasons I agree that he did play a significant contribution to Italian unification but there are other crucial factors, namely Garibaldi’s role in the south and the role of other European powers which contributed to the unification of Italy. It is clear that without these other contributing factors, Cavour would not have been able to solely unify Italy and the fact that it wasn’t his original aim, demonstrates that his significance was almost an accidental one.