the customs union among the german states to promote economic unity was.....?

Answer 1

The German Zollverein (translation, "customs union")

The starting point was Prussia's abolition of all internal duties and its adoption of an external tariff in 1818. In the next few years a number of other German states followed the Prussian example. Bavaria and Württemberg set up a customs union in 1828, and by 1830 four separate customs unions were in existence. Prussia then sought to break up the local customs unions and attach them to a general customs union, the Zollverein. The coverage of the Zollverein increased until, by 1871, it included all the German states.

Answer 2

Zollverein, literally "toll union."