[Mojave]

Very plainly you meant the common law came from the states

You lie.

Precedents, standards and customs evolved over time from multiple sources, they aren't "made up" by courts.

[Republican Party Reptile]

Precedents, standards and customs evolved over time from multiple sources ... may be basis for a formal legal framework, but by themselves these aren't laws until the courts codified them into a system of jurisprudence.