Answer:
C
Step-by-step explanation:
A. is a base, I believe, B. is 'frontier presidios', which is another word for Mexican Fort, and D. is just the military.
Now if we look up militia, we get "A militia is generally an army or some other fighting organization of non-professional soldiers, citizens of a country, or subjects of a state, who may perform military service during a time of need, as opposed to a professional force of regular, full-time military personnel, or to members of a warrior nobility class"
Which means in normal person speech "an army of unprofessionals (Not option D) that have a loyalty to their state or country, and perform services related to military (not option A) to assist in times of need. "