Well, that makes it crystal clear.
I had some commentary from a couple Brits on the way things are organized (?) over here.
We have separate police departments at the town/city, county, and state levels, in addition to federal law enforcement agencies such as the FBI and US Marshalls. Also, each state has its own drivers license. It doesn't make for a homogeneous system.
Basically, we have 50 independent political entities joined together in a federal union.
The key is that the states are supposed to retain sovereignty over their internal matters in all areas where the federal government does not have specific Constitutional authority. Unfortunately, since our Civil War the federal government has continually expanded and encroached into areas not allowed by the Constitution.