Too much debt? Devalue the peseta and drachma. Exports increase, imports decrease, unemployment adjusts. Lenders knows that they must charge higher interest rates to those countries.
That process can't happen anymore. So the same behavior that was mildly damaging before suddenly became very, very damaging. Neither Southern nor Northern European leaders fully recognized this problem when they created a single currency.
I've never really gotten why one country would want to share only a currency with another country, while leaving their social and economic policies independent. But now that that's happened, the combination gets to stand or fall as a whole.
Of course Italians and Spaniards don't have any desire to become Germans, and vice-versa. The currency part was easy - the "harmonization" part will take generations if it happens at all.
Germany agreed because reunification had been a dream for decades.
You will find that "collapse of the East German state (DDR) after the wall was brought down" is more inline with history.
... and prevent them for going Nazi again ..... ?
Sorry but this is wrong on at least two level:
1. Nazism is a political movement (regardless of your political inclination). And thus not directly impacted by having a currency or another. 2. Nazism is way too present, still, in the memories for it to make a come back in Germany as a legitimate political endeavour.
The creation and adoption of the Euro currency was a natural political continuation of the ECSC (see http://en.wikipedia.org/wiki/European_Coal_and_Steel_Communi...) and extension of the European Union. Now yes the initial intend is to prevent future Pan European war through economical cooperation, but not solely to prevent Germany "to go Nazi again" (despite the comment one can read about French President Mitterrand and British Prime Minister Thatcher regarding the future of Germany in Europe, neither of which should be regarded as anything but power hungry political leaders).
Actually, to "force members to stop such ways" was the plan for the EUR/ECB/Maastricht from the beginning. But it's either not working out as planned, or taking way longer than planned.....
