QuietEvening, there is a unified EU currency, but not a unified debt or fiscal structure, so the weaker countries have paid comparatively high bond yields, and therefore the big banks in the stronger countries hold a shitload of Greek (And Spanish, Irish, etc.) bond debt on their books as assets. Conversion back to the drachma in Greece means default (Or something just about as bad, when the debt is converted at an official exchange rate and the value of the drachma immediately plummets to parity with the Zimbabwe dollar), dragging the finances of the healthy countries down with the bad.