Problem with Indians and Cavalry

[Belisarius7]

I just started playing BOA, but I've read up on most of the main topics of supply, command points, and detection.

My main problem is when smaller enemy units start penetrating deep into my territory and lay waste to the regions in my rear. I leave garrisons in my cities but I can't seem to protect the territories surrounding them. The raids come from Natives or even a sometimes small units of British militia or Cavalry.

This is especially devastating in the beginning of the 75-83 campaign when most of my units are with Washington.

Any advice would greatly appreciated.