I have found the easiest offense against the indians is the same one that the English/the United States used in real life.

Send a stack of assorted (mostly cheap) infantry into their territory with a general . Create a fort. The stack doesn't have to be full, a half stack will do. The indians will attack twice depleting their entire army stacks. Counterattack with a full stack of assorted units (including the units in the fort).

I have never lost a single battle with the indians since using this. This also keeps the indians from sneaking into your territories and causing trouble.

Some people may think this is lame but it has worked for me. Some of the battles were pretty interesting, reminding me of the cowboy and indian type movies with indian lancers circling the fort , waiting their turn to get in.