The "or else" is actually on rather shaky grounds considering the national debt. For the sake of argument if certain countries decided to stop buying US treasury bonds the federal state would be insolvent about 5s later. Certainly a default of that size would destroy the economy in every single country pretty much except maybe Cuba and North Korea.

The EU (and Europe) will have to lean East until Germany remilitarizes. US will find itself alone with enemies on all sides.