essay topic: if the U.S. government collapsed in 2018

[DontRaisePlz]

For my government class, I have to write an essay around this prompt:

"If you were told the U.S. government completely collapsed in 2018 based on *A REASON THAT CURRENTLY EXISTS TODAY*, which reason would you venture to guess that would be?"

I can pick anything as long the essay is informed and coherent. Budget deficit, war, oil, North Korea, whatever - as long as its not aliens, apocalypse, rampant epidemic, sun explodes, etc.

Any suggestions? I just want an outline, maybe a good source where I research the issue.