What caused the eurozone crisis?

After five years of crisis there are now signs that the eurozone economy is recovering, but it is far from being back to normal. The authors of this CEPS Commentary sound a note of caution: although progress has been made with the banking union and new institutions like the European Stability Mechanism (ESM), more needs to be done. The eurozone crisis may be in remission now but when interest rates start to rise, or if confidence evaporates again due to global shock, the systemic cracks could reappear at an alarming rate.