PoS has a fatal flaw: a person who wants to fork a PoS network simply needs to pay other people in the network for the private keys to their older, spent, transactions. Alternatively, any kind of security breach giving access to used private keys would work. After you have enough keys that had coins in them at a certain point in time, you can &quot;grind&quot; the history forward, and create an alternative chain with your chosen transaction history.