You can choose to resolve land battles on a strategic level or using tactical battlefields. For the tactical option set the tactical battle control on the preferences screen to Manual.  For the strategic option set this control to Automatic. Once you are on the battlefield using the manual option, you can still choose to resolve the tactical fights yourself or order your advisor to do so. Even if you give control to your advisor for part of the battle, you can take it back if necessary. Regardless of the mode of resolution, the same rules apply to all battles and a battle report will be shown to you to check results after the fight.

A human who is experienced with the tactical option may find that the computer does not fight as well as the human expects when the battles are resolved strategically.  Generally it is a good idea to attack with slightly larger forces when using strategic combat resolution.