Final answer:
The most successful economic integration is the European Union, which has fostered regional stability and economic collaboration, including the adoption of the euro as a common currency among its member states. Option number C is correct.
Step-by-step explanation:
The most successful economic integration is c. the European Union. After World War II, European leaders sought economic ties that might prevent future wars, resulting in the creation of the EU. This integration started as a free trade association and developed into a full economic union.
With ambitions that included the introduction of a common currency, the euro, the EU aimed to foster the free movement of goods, labor, and capital across member states. Despite Brexit, which saw Britain leave the EU in January 2020, the EU remains a paramount example of regional integration.