Final answer:
The euro is the single European currency that unified the marketplace by replacing 12 national currencies. Adopted by most EU countries, it facilitates trade and movement but limits individual monetary policy control.
Step-by-step explanation:
The euro is the single European currency that replaced 12 national currencies and unified a huge marketplace. The adoption of the euro was a significant move by the European Union (EU) towards closer economic integration. After World War II, European leaders saw tighter economic ties as a way to prevent further devastating wars. The initiative started with a free trade association and eventually developed into the EU—a full economic union. By the early 2000s, the EU introduced the euro, phasing out national currencies like the German mark and the French franc among others. Great Britain was one of the few members that kept its currency—the pound sterling—until it completely left the EU in January 2020.
The euro allows for easier trade and movement across Europe but also means that nations using it have ceded control over their domestic monetary policies to the European Central Bank. While the euro has been adopted by most EU members and even some non-EU countries, a few European nations have opted to keep their own currencies. The introduction of a single currency like the euro, while simplifying transactions and fostering unity, also requires members to forego certain economic freedoms and align with broader EU monetary policies.