It all started when Bitcoin traffic increased due to the new popularity of the cryptocurrency. The increase in traffic caused some difficulties that different Bitcoin developers were trying to solve.
What emerged were two different solutions that split Bitcoin developers into two groups. Each group proposed a different technical solution to the problem, and neither group could come to an agreement that would keep the Bitcoin community united.
This means that any transactions that were made before August 1st, 2017 exist on both blockchains, and any that occurred after are unique to that currency type. This means that if you were a Bitcoin owner on August 1st, 2017, you now are also the owner of Bitcoin Cash.