Heyho,
this is gonna be a bit of a "yes and no" answer 
The military is neither as indirectly controlled as in the first 2 The Settlers games nor as directly controlled as in e.g. The Settlers 3 and 4.
We've just started off our next topic in regard to articles over on the The Settlers Alliance which is, coincidentally: the military.
We will start introducing various buildings related to the military path and have articles going in detail regarding recruitment, control, military leaders etc later down the line.
So, only a short reply here:
Any offensive actions require direct player input with you controlling groups of soldiers, while defending can be done in a more passive, indirect manner.
A stable, well-oiled economy and logistis system will be needed to produce the equipment needed for the soldiers - also due to all workers in the game now needing food (and not just the miners).
There is, however, no dedicated mode where certain features are completely changed or deactivated (you can play without opponents, though).
Hope this sheds some light on the topic - more later
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