Basic Army Question: MPs vs. Police on-Base?

Can anyone explain how is it that there are Military Police (MPs) on-Base under the Provost Marshall’s Office (PMO) and Police (Dept of Army Police) under the Dept of Emergency Services (DES), but… do the two ever meet? Is there any organizational structure placing one under the other? Is one only Garrison-wide, perhaps? Are the MPs limited in authority? How does this all work and inter-relate? Thanks for helpiing this civilian have a better understanding.