Answer:
The use of a single currency called the Euro
Step-by-step explanation:
Spain belonged to a regional or continental Supranational Organisation also know as the European Union.
One of the benefits Spain gained when they joined the European Union was that there was an boost to the economy of Spain based on the freedom of trade with other countries that were also part of the European Union.
One of the identity challenges Spain faced as member of the European Union was the use of a single currency called the Euro.
The European union placed a lot of emphasis on the usage of Euro as a single currency in their member countries as oppose to the usage of the national currency in that country. This has resulted into a challenge in the identity of their member countries, a lot of unemployment and difficulty in trading.