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A fork is a situation in which new rules or changes are made to the blockchain network and there is a deviation from the older version of the chain. A hard fork occurs when the changes to the code are so significant that the incoming new blocks are no longer compatible with the earlier blocks. Hard forks are also sometimes carried out on purpose by the entire set of nodes of a blockchain to leave behind the older network and move to a newer, more efficient one. These forks allow the network to evolve beyond its initial realm by adding new features and functionalities.