There are numerous reasons why Bismarck was more successful than the revolutionaries in unifying Germany but the most important of these he identified himself by saying: „not through speeches and majority decisions, will the great question of the day be decided, that was the great mistake of 1848-but by iron and blood.
The first factor leading to the failure of the Frankfurt parliament was their unclear aims and splits among them. They could not decide upon the eventual shape of the state. Would there be a Klein Deutschland without Austria or a Gross Deutschland which included Austria? Also the question of how much power the princes would have remained unsolved. Conservatives wanted constitutional decisions to be implemented by the individual princes while liberals wanted the parliament to have more power than the kings. All in all they were too divided to get to a conclusion and organise a clear civil administration.
Bismarck on the other hand was politically and ideologically a strong leader. He knew exactly what he wanted and he used whatever means necessary to achieve his goals. He was a Realpolitiker through and through. This included making sure the monarch and the state being preserved plus making sure that unification would take place under the Hohenzollerns, not Austria. He did that by making Italy an ally and defeating Austria with the Prussian army in 1866.
Another big mistake of the 1848 revolutionaries was the failure to mobilise an army. Instead they relied upon the goodwill of the Prussian King Friederich Willhelm IV to provide them with an army. By 1849, the Austrians were ready to crush opposition and to bring back the old rulers and restore the Austrian dominated German confederation. With no army of their own, the Frankfurt parliament was severely weekend and not strong enough to resist Austria. Also, although King Frederick William IV of Prussia