The splitting of Ethereum into separate blockchains. A hard fork means that the two chains are not compatible. This occurred three times from 2016 to 2022. See
Ethereum and
hard fork.
Ethereum Classic
In 2016, the original Ethereum became Ethereum Classic and adopted the ETC symbol. The newly-spawned network became the dominant Ethereum chain and retained the ETH symbol. See
Ethereum Classic.
London Hard Fork
In 2021, the London hard fork added five changes to Ethereum (ETH) and required all nodes to upgrade in preparation of the split in 2022. See
London hard fork.
A Major Split in 2022
A dramatic change in protocols, Ethereum changed its consensus method from proof-of-work to proof-of-stake. See
Ethereum 2.0 and
Ethereum PoW.