Initially, the Bill of Rights only applied to the Federal Government, and the states had no obligation to follow it. The constitution only controlled the federal government.
When the 14th amendment passed, it extended the rules down to the states too. The Supreme Court agreed, but only selectively enforced them. More here:
https://www.law.cornell.edu/wex/incorporation_doctrine#:~:text=Overview,applies%20both%20substantively%20and%20procedurally
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