A hard fork is a phenomenon where a blockchain network undergoes a radical change in its protocols that triggers a split, birthing two separate chains, the original network, and the “fork” network. A hard fork may be intentional or come off as an accident. Oftentimes, forks happen whenever developers encounter differences in the way they want a project to move forward or when its community feels that the protocol should follow a different direction.
One of the earliest examples of a hard fork is the Bitcoin (BTC) and Bitcoin Cash (BCH) debacle where an initial divide within the community to increase the block size for BTC led to its hard fork. BCH went to implement a larger block size of 8 megabytes, allowing the new Bitcoin fork to include more transactions in a block. The BTC community didn’t believe in the same approach, claiming that increasing the block size would not be a feasible long-term solution since it can further strain the network.
Some other hard forks are implemented to amend blockchain security concerns, introduce a new version of the network, or reverse previous transactions. For instance, the Ethereum community was forced to launch a hard fork in 2016 in order to roll back millions of tokens stolen by hackers from its Decentralized Autonomous Organization (DAO).