A chain split is the division of a blockchain into two separate networks that share the same history up to a certain block but follow different rules afterwards. It usually happens after a contentious hard fork, when part of the community upgrades to new rules and the rest keeps running the old software, so each group builds its own chain. Holders typically end up with coins on both chains. Well-known examples are the 2016 split of Ethereum and Ethereum Classic after the DAO hack, and the 2017 creation of Bitcoin Cash from Bitcoin over block size. Splits can also happen briefly by accident when software bugs cause nodes to disagree, which is usually resolved by a chain reorganization. Also see Fork.