Residential and commercial buildings stand on the city skyline seen from the "Vor Frue Kirch" church tower in Copenhagen, Denmark, on Thursday, March 13, 2014. Denmark's central bank, the country's financial regulator, and international credit-rating companies have warned since at least 2009 that so much one-year debt makes the $550 billion market vulnerable to a sharp decline in investor demand. Photographer: Freya Ingrid Morales/Bloomberg via Getty Images