Complex sentence: Changes in philosophy and technology have been reflected in changes to military tactics; in contemporary military science tactics are the lowest of three planning levels: (i) strategic, (ii) operational, and (iii) tactical.
Split into simpler sentences: Changes in philosophy and technology have been reflected in changes to military tactics. In contemporary military science, tactics are the lowest of three planning levels: (i) strategic, (ii) operational, and (iii) tactical.