I can elaborate on any point if interested, but this is covered in the parent.

1. They would drive the price up way past market price in an attempt to make such a large purchase. The cost of a large, rapid purchase is far, far from market price. Only a fraction of the market is willing to sell at current price.

2. If a country wanted to run on Ethereum, they could clone it, since they are giving up the benefits of a GLOBAL system when they take it over.

Lmk if you have any questions. Pretty interesting topic given the insane ETH valuation atm, in contrast to, say, Algorand. Network and first move effects, I guess.

The etherium developers and community have made relatively clear that if someone were to attempt such a thing, the non-malicious members of the community would just fork at the direction of the developers to a chain that is identical except that all of the etherium staked by the attacker is redistributed among the non-malicious verifying nodes, as it would be once the consensus process concluded that an attack was being carried out in a <51% attack scenario.