Originally, the Bill of Rights didn’t apply to the states at all. This changed with the Equal Protection Clause of the 14th Amendment and the development of what is called the Incorporation Doctrine. The Supreme Court “incorporated” each right against the state and local governments as those governments were sued over them.
This process has taken decades because the courts can’t rule on whether (x) applies to the states unless a state gets sued over (x). The Third Amendment, for example, still isn’t fully incorporated.
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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