The creation of the Zollverein in 1833 is generally said to have helped develop a sense of unity among the various states that existed in what is now Germany.
The Zollverein was essentially a free trade area that was made up of various states in what is now Germany. By breaking down the barriers between these states, the Zollverein helped create a sense that the states were all part of one greater whole. In addition, the Zollverein encouraged the idea that the German states were distinct from Austria. This gave the German states both a positive sense of identity (since they were all part of this union with no trade barriers and with common weights and measures and stuff) and a negative sense of identity (they were not part of Austria).
By doing these things, the Zollverein helped to create a sense of unity among the states that would later unify and become Germany.