'Without the decline of Austria neither the unification of Germany nor the unification of Italy would have been possible.' Comment. Background Italy
The Austrian Empire has been widely considered the most powerful force against the unification of Italy as it controlled the mostly Italian-speaking areas that now are the northeastern parts of the modern-day Italy. One of the major leaders behind the Risorgimento, the Piedmontese Camillo Cavour, had struck a deal with Napoleon III: Cavour would spark revolts in Lombardy and French troops would come to his aide once the Austrians responded with military force. In the ensuing war, Sardinia-Piedmont would take Lombardy and Venetia with the help of the French, and they would then aquire Savoy and Nice as a reward.
The revolts, however, were insufficient to provoke Austria, but when Cavour sent troops to Lombardy, the Austrians immediately mobilized their army after he refused to retreat. This was a suitable excuse for Napoleon´s intervention, and the combined forces of Piedmont and France defeated the Austrian forces in two successive battles, capturing Milan in the process.
Nevertheless, Napoleon decided to abandon the cause after witnessing the heavy casualties of the second battle; he also realized that the conquest of Venetia would be costly and was unsure about the ramifications of the Piedmontese expansion, which could make it a potential threat to France. In addition, Prussia may have recognized this and supported the Austrians in the war. Napoleon signed a treaty in Villafranca with the Austrian Emperor; the French would stand down and let Piedmont keep Lombardy, but since Napoleon failed to capture Venetia, he would not receive savoy and Nice as originally planned.
Cavour was upset by the French betrayal and resigned from his position, though he returned later. Despite the lack of French support, the Piedmontese managed to obtain most of the states of central and northern Italy, with some of them joining without resistance. Napoleon approved of this, although only after receiving Savoy and Nice as originally planned.
The following stages of the war was completely internal. Giuseppe Garibaldi, a veteran who had fought the French and Austrians about a decade earlier, wanted to take back his hometown of Nice from the French. Cavour, however, persuaded him to take over southern Italy and annex it with the now-expanded Sardinia-Piedmont. Garibaldi achieved several swift victories with his Red Shirts, capturing the capitals of Sicily and the Italian mainland. The increasingly popular commander now had thousands of volunteers help his campaign. Cavour was suspicious of Garibaldi, concerned that he might try to become a rival of Sardinia. Cavour quickly defeated the Pope´s army after attacking the papal states and finally defeated the King of the Two Sicilies together with Garibaldi. As promised, the land conquered by Garibaldi was handed over to Sardinia, forming the Kingdom of Italy. Cavour died shortly after.
To complete Italy, the King joined the Austro-Prussian war (which, in turn was a step to unify Germany) on Prussia´s side. Venetia was then annexed with Italy, and the last phase was conquering Rome. As the French had to pull their troops stationed there back to France to protect it from Prussia, the Italian forces could more or less just march in as there was no resistance. Rome then became the capital of the united Italy in 1870.
Austria, Prussia, and the smaller German states had been loosely united into the German Confederation in the Congress of Vienna in 1815. In 1850, the king of Prussia suggested the creation of ´the Prussian union´-but Austria promptly declined as a Germany dominated by Prussia would undermine Austria.
However, Prussia had already gained the upper hand by the ´Zollverein´- a customs union which was established to make free trade easier among its members, which included all German states other than Austria and four others by 1954. Since the German Confederation consisted of a large number of small states, all incoming goods were previously taxed several times as they passed through the area. This made the profits of trade very bad- but with the Zollverein, the tariffs were a lot cheaper and this strengthened Prussia while Austria was weakened.
The new Danish constitution, created in 1863, seemed to claim the territories of Schleswig and Holstein as its own, resulting in an angry German reaction as Holstein was part of the Confederation and Schleswig was only ambigously Danish. Despite demands from Austria and Prussia to change the constitution, the Danes ignored them, only to be shortly overrun by their armies. In the convention of Gastein, in 1865, Prussia and Austria agreed to administer Schleswig and Holstein, respectively.
In the meantime, the minister president of Prussia, Otto von Bismarck, had secured neutrality from the French, in return for some land in the Rhine. Also, in 1866, he had promised to give Venetia to Italy as a reward, if it were to provide assiatance if a war broke out within three months.
Shortly after, Austria started rearranging Hostein. Bismarck considered it a violation of the Gastein agreement and declared war. Most of the Confederation joined Austria´s side, but the army of Prussia had superior weapons and tactics, and quickly won the conflict, later known as the Seven Week´s war. With this victory, Bismarck created the North German Confederation with himself as its chancellor and the King of Prussia as its leader. Schleswig and Holstein, among other, were annexed.
Shortly after, France declared war on Prussia due to a disagreement with the Spanish throne. France was quickly defeated. A peace treaty was signed in Versailles, and the German Empire was formed-this included all German trritories other than Austria, as well as some French territories.
In each of the unification processes, Austria heavily opposed their respective efforts. In both of them, it was the greatest obstacle that stood in the way, as much unlike France, it was against them from the beginning. However, I would say that Austria´s failure to stop the unifications in Italy and Germany was inevitable as it was faced with both the French and Italians in Lombardy, and the Prussians and Italians in the German unification, where it was probably outnumbered and overpowered. Furthermore, other than Lombardy, most of the Italian process took place internally, with Garibaldi fighting in the southern states of Italy and Cavour against the Papal states, with no Austrian intervention going on.