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In page Customs union:

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In 1834, 18 states joined to form the German Customs Union with Prussia as the main leader. Thereafter, this alliance was further expanded to all German-speaking regions[citation needed] and became the All-German Customs Union. The contents of the alliance convention included: abolishing internal tariffs, unifying external tariffs, raising import tax rates, and allocating tariff income to all states in the alliance in proportion. In addition, there is a customs union between France and Monaco, which was established in 1865.