How was it accepted by people so quickly?
Bitcoin is not yet accepted by that many people!
And you are forgetting the history of money. The "medium of exchange" has not always been issued by the government or backed by the centralized banking system. It has changed a lot and evolved into the centralized fiat system that we know today and now we have the decentralized version of money in digital form once again. It is like a full circle.
As pooya87 said, not so long ago usd was backed up by commodities (gold). Things changed in 1971 when united states abandoned Bretton woods deal and usd was no longer backed up by gold, becoming a fiat currency.
A fiat currency is a currency backed by nothing, only in government authority and the trust people have in it.
Will its emergence be the country's fiscal sovereignty and monetary sovereignty? If the government strengthens its control in the future, can it continue to its current development?
About fiscal sovereignty, I think it is quit the opposite.
Now governments are free to print out money and spend more than they have. If bitcoin is ever to be used by governments, they will not be able to do so, which is a loss of sovereignty