What caused the Ethereum Fork?
Following an incident in July 2016, the Ethereum network underwent a fork. At that time, attackers exploited vulnerabilities in the smart contract code of a prominent Ethereum application called The DAO. In response to community concerns, the Ethereum Foundation implemented a hard fork to reverse all transactions related to The DAO and allow original DAO contributors to recover their funds.
While many communities supported Ethereum's hard fork, some chose to continue operating on the original Ethereum blockchain. This blockchain became known as Ethereum Classic.