Greece's return to the bond markets last week was a symbolically important moment for the euro crisis. For the country at the center of the crisis to draw €20 billion ($27.77 billion) of foreign demand for a five-year bond yielding under 5% shows that the market now believes Greece will stay in the euro zone, that it won't collapse into chaos and that any further debt relief will be provided by official rather than private lenders. A year ago, there were few takers for that bet.

But this was only the latest in a series of...