The idea that a single government could buy all of the Bitcoins is unpractical in theory.
This is because many people who will hold Bitcoin would never sell it. It would literally take a hack of epic proportions or a critical design flaw in the blockchain technology which powers Bitcoin in order for such an event to occur.
As an individual or joint effort any government could easily buy up a big chunk of the Bitcoin market. They could even destabilize the market by buying enough to create FOMO, then dump it back on the market later. This has the potential to damage moral, confidence and trust in Bitcoin. In fact some advocate that this is what may have happened when each Bitcoin shot up to $19,600 USD last year.
* There are a few million coins that can never be gotten because they sit in wallets where the private keys are missing, Because of this owning all the coins would actually be impossible. At most, an entity can only own the coins that are currently tradeable on the market.
* Almost 4 million Bitcoins are still not mined.
* Here is how things could change if something went wrong with Bitcoin (like a government buying a majority of it). A fork of bitcoin protocol would be instituted and a clear fresh start would occur. The technology of blockchain cannot be contained.
Nevertheless, it is not totally unreasonable to consider that a government or any large central power could focus on damaging or breaking the Bitcoin network. Fortunately there are always solutions including the fact that the satoshi white paper is in the public global domain and that it could easily be relaunched and called something else.
ARE THERE OTHER WAYS BITCOIN COULD BE BLOCKED?
Are there other realistic threats to blockchain technology? Of course there are some and maybe even a few that have not yet been identified. For instance, the biggest threat to crypto may be the banning certain types of mining like ASIC boost that require special equipment.
Other ways to influence, limit or block Bitcoin exist:
a) Prescribing the full public transparency of all transactions and for what reasons those transactions are executed
b) Requiring that the “mining” algorithms used are no longer allowed or do not deliver additional cryptocurrencies as a reward ending the stimulatory creation or the progress of the blockchains
c) Prescribing an effective system of governance (including ALM and KYC) for all cryptocurrency blockchains
d) Massive taxing of every cryptocurrency transaction going through the blockchain.
d) Forbid the use of cryptocurrencies as a pseudo fiat currency in all financial transactions. (3)
The devaluation of fiat is happening worldwide, the value in many countries is backed mainly by belief and the debt continues to rise. The printing of more fiat creates a mounting problem that could be disastrous. Bitcoin has a limited supply of tokens and is not subject to this practice.
Sources:
1. The Balance
https://www.thebalance.com/is-the-federal-reserve-printing-money-3305842
2. Hidden Money That Keeps the Word Afloat
https://www.thebalance.com/money-market-instruments-types-role-in-financial-crisis-3305528
3. Alphons Ranner, Independent finance & governance specialist at Sovereign (on Quoro.com)