Having discussed it with you, I believe your question is simply "How do I implement a 3D camera in directX?" The principles are the same regardless of the genre of the game (i.e., the "strategy game" detail is not relevant). And the example video we looked at together is just 3D, not "somewhat 3D".1
In any event, how to implement a camera is something that comes up quite a bit. This answer from Josh Petrie is pretty good and has some handy tutorial links:
There are several ways of going about this (see tutorials here, here
and here for example, with plenty more available on the Internet via
Google). The technology used in the resources you may find online may
vary slightly (in terms of D3D, XNA, OpenGL, et cetera), but the
underlying principles are going to be the same:
your camera object maintains its position and its direction, and
optionally another pair of vectors that, alongside the direction, form
an orthogonal basis for the camera's coordinate system.
your camera's public API exposes methods for yawing, pitching, and optionally
rolling the camera around it's basis vectors -- the act of adjusting
the camera orientation will update the basis vectors for subsequent
use.
You can elect to store the vectors directly, or recompute the
underlying view matrix every time, as you need and prefer. There's a
lot of flexibility to the technique, so if you need help beyond those
general steps you may want to post a new question with a more specific
query.
1It may be that you're thinking of that video (at 3:50) as not truly 3D because the game does not give the player control over the camera.