Metternich saw the zollverein as a form of a threat and said, "little by little, under the direction of Prussian and by the necessary formation of common interests, the states which make up the Union will compose a more or less compact body, which in every matter (and not simply in commercial affairs will act and vote in common on the basis of pre arranged principles. " The fact that Austria is worried about the Zollverein shows it's significance, furthermore William Carr has called the Zollverein “The mighty lever of German unification.” while John Bowring described it as the Germanisation of the country. Austria was completely opposed to a unified Germany and wished to keep Germany as small states individually ruled by a monarch. This way the states would be weak and could be highly influenced by Austria. The zollverein "Germanised" the country and helped to unify the states and make it into a "compact body" thus making it very difficult for Austria to control. From my own knowledge i know that much of Austria's territory consisted of Italian states and when they had mini in an attempt to overthrow their monarch and unify Austria sent in an army to put down the rebellion as they did not want unification. The same principle occurs here with the German states.
Austria wanted to stop Liberalism and Nationalism in order to secure their control of the German states how ever In 1815 Metternich became worried about the growth of Liberal and Nationalist student societies while 1819 Carlsbad Decrees banned student societies and censored newspapers and the following year the power of the Diet was increased so that soldiers could be ordered to stop the spread of new ideas in any of the German States.
Revolutions of 1848 were the first attempt to challenge Austria’s political power in Germany. A new German parliament was started in Frankfurt how ever it failed. The Zollverein was arguably the core of these actions as it, in a way encouraged Nationalism and Socialism thus causing these uprisings as the Zollverein was a prototype of a ‘united Germany’ under Prussian control that excluded Austria and helped the country become more powerful, since it was a was a major breakthrough for economic unification within Germany.
More evidence to show that the zollverein were successful in changing the economic balance of power between Austria and Prussia is that the Austrian minister of commerce said, "Austria has, above all, one thing to prevent, namely that the Zollverein." and also said that, "If Prussia were to see her supremacy assured for so long a time, she would scarcely be persuaded to enter the customs union with Austria." This shows that Austria was quite desperate to join the zollverein as their economy was deteriorating.
On the other hand the Zollverein were only partly successful in changing the balance of power between Austria and Prussia. They did not provide a full unification of Germany or even partly unify it. It only provided some foundations for a later unification and so it was arguably not that much of a threat to Austria, although it gradually had more influence on both countries after more states joined it and after it spread to Europe. In addition if the Zollverein was not formed than there would not be a vast economic change in Prussia and so there would not be much of a change in it's economic power and it would not be able to later challenge Austria as it did. This highlight the importance of the zollverein in terms of it changing the economic power of Prussia and gradually changing the balance of power between Austria and Prussia.
Although the Zollverein was a very important factor there were also other factors which influenced the balance of power between Austria and Prussia. For example Prussia had expanded it's territory in the face of Austrian opposition and gained more territory in the peace settlement of 1815. This increased Prussia's power and made it the dominant state in Northern Germany. This is an important factor as it made it possible for Prussia to be the only state capable of challenging Austria and made it easier for the Zollverein to be controlled by Prussia as it was the biggest and most powerful state around Northern Germany. In turn this helped to increase Prussia's power both economically and in military terms and made it more capable of challenging Austria.
Another reason as to why Prussia gained power was due to the victory against Austria (1866) however this factor is not as important as the zollverein as the zollverein helped Prussia to actually become strong enough to challenge Austria.
In conclusion The Zollverein was very important in changing the balance of power between Austria and Prussia and was the most important factor in doing so. This is because the Zollverein made it possible for Prussia to stand up to Austria economically and provide a small form of unification making Germany more likely to withstand an invasion from Austria later on and increase it's economic power so it would be able to economically challenge Austria as well. This obviously increases Germany's power and in turn slightly cripples Austria as it isolates Austria from the Zollverein and in this form slightly cripple it economically.