According to the video linked here, only 3 mining pools control 51% of bitcoin processing power.
When the international central banking cartel finds the most profitable moment, they will set energy policy for our US and European governments which forces these three mining pools to shut down. If any of those mining pools are in countries that will not cooperate with ESG mandates then the mining pools will be destroyed in a drone strike under the pretext of anti-terrorism or in some made up war under the pretext of human rights and democracy.
Then a much smaller group of mining pools controlled by the cartel will be in control of the 51% processing power required to double spend.
At that point bitcoin will just be another central bank digital currency controlled by the central banking cartel.
This attack could be accomplished today. The only reason they haven’t done it yet is because now is not the most profitable moment for the international central banking cartel to take control of bitcoin.
I don’t think this type of attack can be executed against Cardano. I think the attacker would have purchase more than half of all staked ADA in order to execute a 51% attack.