What happens if the FED Government were to collapse?

The hard problem is invasion - or, more or less equivalently, takeover by internal warlords. Broadly, it's what people worry about when they talk about a "power vacuum", and the motto is, "if they don't do it, somebody else will". Of course, only talking about removing the Federal government, leaving the state governments in place. I think we would become a collection of smaller countries, as Europe is. The American Federal government is tenacious, murderously so, so don't expect it to disappear before it has murdered hundreds of thousands or millions of Americans. Something similar was attempted in 1861 and failed after half a million Americans had died, and the man in charge of the Federal government at the time is now considered our greatest President and an example for the Federal government to follow.