Final answer:
The term for European countries uniting to reduce trade barriers and encourage trade amongst themselves is called the European Union (EU) (c).
Step-by-step explanation:
When several European countries band together to reduce trade barriers between them to encourage trading among themselves, this is known as the European Union (EU) (c). After World War II, the EU started as a free trade association and evolved into a common market, eventually becoming a full economic union. One of the EU's significant goals is to eliminate barriers to the free movement of goods, labor, and capital across member nations. Established goals such as introducing a common currency, the euro, and phasing out national currencies, like the German mark and the French franc, have been key developments, although some members have retained their own currency. The EU aims to foster economic integration to prevent conflict and improve prosperity among member states. Therefore, the correct answer to the question would be C) European Union.