This may help with some small understanding.... but probably not.
The United States was created with the idea that Individual Sovereignty must be able to co-exist with the idea of a united, federated, country.
Therefore the 13 originial Colonies that became States maintained their own practices and governing bodies.
This idea was paramount on every level of goverment. Nobody wanted to give up power to the next higher "level" of government.
So, if you add the idea of the American archetype of "rugged individualism" to the ingrained bureaucracy of any govermental system, you get a continuing overlapping system of agencies and governments from the lowest (rural counties without any townships?) to the highest (the Federal government).
For instance: the Village of Williamsville has all of its own government agencies. And even though it is today ten times bigger - it is located within the Town of Amherst, which also has all of its own agencies - both Village and Town have overlapping agencies that service both.
They are both located next to the City of Buffalo which also has its own agencies plus some agencies that overlap and serve the Village of Williamsville and the Town of Amherst.
They are all located withing Erie County which also has its own agencies which also serve the needs of the aforementioned governments.
Erie County is located within New York State, which also has all of its agencies, etcetra...
And they are all located within the United States of America which has more overlapping agencies that you could ever shake a stick at....
Just to bring it to the point. Each governing body has its own police force and as you get higher in the hierarchy, you get multiple police forces serving multiple functions.
It all stems from the desire of each governing body to control its own litte (or big) "fiefdom."
And that is all based on rugged individualism and the idea that each citizen has sovereign rights unto themselves.
Okay?