A chain split happens if the community doesn’t uniformly upgrade or if there’s a contentious hard fork. Like a fork in the road, some nodes follow one rule set while others follow another, producing two separate histories from the split point onward. Each chain has its own blocks, transactions, and potentially duplicate coins.

Notable examples include the Bitcoin–Bitcoin Cash fork in 2017, where one group sought larger blocks, leading to separate networks. Chain splits can be intentional (contentious forks) or accidental (software bugs). Users must decide which chain to support, and if they held coins before the split, they typically receive coins on both forks—though the new chain’s value is never guaranteed.