At the most basic level, Bitcoin Cash was born because the community
could not agree on how to scale. One side wants to scale off chain (BTC)
and the other wants to scale on chain (BCH). The motives, incentives,
politics, technical realities and all that I'll leave it to you to
research an make up your own mind on.
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The story behind that is very anecdotal depending on who you ask. My
interpretation is that it's mainly about blocksizes and scaling. One
group though the solution to scaling was increased blocksize to allow
more transactions per block, while the other side saw level 2 solutions
like lightning and segwit as the solution to scaling.
