And what’s the main use of cash from the perspective of the US government? And what makes cash have value? And what has been the history of money thus far that has led to this junction?

Transacting for goods and services. Cash has value because you get arrested if you don’t have enough to pay taxes.

I totally agree. Cash has value because it’s backed by violence.

Oh no the state has a monopoly on violence what a bad thing. I much prefer the natural way where your right to property ends at the tip of my spear.

Everything privately held that has value is backed by the threat of violence.