The original intent on the federal government was to provide protection to all of the states. From there on in it was the states that governed themselves and passed laws as they saw fit. The only reason why the fed wield so much influence state to state are the federal tax dollars in terms of aid and funding that would quickly dry up if the states did not adhere to federal command. If I recall correctly didnt the feds impose a nation wide speed limit ban, and would curtail transportation funding to any state that would not comply?
Moral of the story, 50 states govern themselves, but fall under the union of the states. the feds have imposed incredible amounts of authority over states that for a century and a half had previously not been the case.