The eurozone debt crisis was the world's greatest threat in 2011. That's according to the Organization for Economic Cooperation and Development. Things only got worse in 2012. The crisis started in 2009 when the world first realized Greece could default on its debt. In three years, it escalated into the potential for sovereign debt defaults from Portugal, Italy, Ireland, and Spain. The European Union, led by Germany and France, struggled to support these members. They initiated bailouts from the European Central Bank and the International Monetary Fund. These measures didn't keep many from questioning the viability of the euro itself. […]