Chain Split

A chain split happens when a blockchain's shared history breaks in two: nodes and miners stop agreeing on which chain of blocks is valid, and the network diverges into two or more independent ledgers that share an identical past up to the split point and then record separate transactions from there on. Each resulting chain runs its own blocks, its own native token, and often its own community and developer team going forward.

Most lasting splits are triggered by a hard fork, a rule change that is not backward compatible. If every miner and node upgrades together, the network simply continues as one chain under the new rules. A split only becomes permanent when a meaningful share of participants reject the change and keep running the old software, so both versions attract enough consensus support, in users, miners, and exchanges, to survive independently. Splits can also happen unintentionally, from a client software bug or a temporary network partition between groups of nodes, though these usually resolve once connectivity or the bug is fixed.

The best-known examples are the 2016 split that produced Ethereum Classic after the DAO hack, the 2017 split that created Bitcoin Cash from Bitcoin, and the 2018 "hash war" in which rival mining factions battled for dominance before Bitcoin SV broke away from Bitcoin Cash for good. For coin holders, a split usually means ending up with a matching balance on both chains, but it also introduces replay-attack risk until each side adds protection so a transaction valid on one chain cannot be rebroadcast on the other.