Dollar/Euro has value ONLY because government says so.
Bitcoin/gold/silver etc have value, because people believe so.
That is nothing like fiat.
No. US government can claim anything about US dollar in the USA. They can force you to anything. But abroad, US dollar is valuable because there is an economy that supports it and indeed
people believe it's valuable.
what about "US can ivade your country (alone or with allies) if you have something they want and you refuse to trade with them in us $"