As European policymakers look at the turbulence ahead in 2017, they are watching the eurozone's bond market with growing concern. A sell-off in government bonds, matching the same trend worldwide, is adding stress to the bloc's already vulnerable economies, especially in Southern Europe . Officials' fears have only been worsened by the sell-off's uneven pace, as some members' bonds have been sold more rapidly than others'. The differences in yield between French and German bonds, for example, has reached levels not seen since 2012, when a sovereign debt crisis nearly brought the currency union crashing down. That debt crisis exposed the "doom loop" created by European banks' tendencies to hold their home government's debt. In theory, the vicious cycle could start when markets lose faith in a government's ability to pay back its debt, precipitating a sell-off of its bonds.