Money is subjective. Like countries, it exists only in people's minds.

Its value comes from agreement by a large number of humans that it is valuable.

A stack of Benjamins would be nigh-valueless to people from 9th-century China.

Not at all. The actual value of money comes from violence. This is objective, not subjective. If you have a certain amount of taxable income in the USA (or subject to US legal jurisdiction) then you're required to pay tax in US dollars: the IRS won't accept Euros or gold or anything else. If you fail to pay then eventually IRS employees will seize dollars from your financial accounts, or seize other assets and sell them for dollars. And if you try to physically stop them then they'll arrest you, or even shoot you.

And to be clear, I don't think this is a bad thing. It's necessary to keep civilization working.

	▲	NateEag a day ago \| parent [-]
		A good point. Thank you. The violence, once enacted, is an objective fact. The threat of violence is still there only due to the collective subjective agreement that countries exist. The IRS would have no functional power if Washington, D.C. and other major US cities were destroyed in a nuclear exchange. I could imagine many citizens still choosing to pay taxes of some sort and/or respect the value of physical dollars in such a scenario, but it would likely not be due to fear of the federal government. Possibly fear of local police, though.