How is historical evidence useful to historian

They use evidence from primary and secondary sources and histories to answer their questions. They have to choose what information is most important and trustworthy as evidence. Historical evidence is not always simple. Sometimes what historians thought to be true turns out to be false. So Basically they examine the piece of history weather it is an artifact or something on paper. Just to determain weather its fake or not.

Explanation:

I hope this helped :)

(Please tell me if I am wrong)

a system of cooperative federalism emerged, as the powers of the federal government expanded.