In 1991, the twelve original member countries of the European Union adopted the Maastricht Treaty, also known as The Treaty on European Union.

The Treaty established the European Union; created the European Central Bank and the Euro; and established the rules for adopting the Euro, also known as the convergence criteria or Maastricht rules.

One of the four convergence criteria required countries adopting the Euro to have "sound and sustainable public finances", defined as a government deficit that was not higher than 3% of GDP and government debt that was not higher than 60% of GDP.

The question here is what was the purpose of this criterion and how does it benefit the European Union as a whole? (Hint: think of the impact of lower deficits and public debt levels on the member countries' ability to borrow.