Complex sentence: Many writings on the subject of espionage jumble the two together as the same thing; but they are different specialties, with different objectives, and a different mindset required from those working in the field.
Split into simpler sentences: Many writings on the subject of espionage often jumble the two together as the samething, yet it is important to understand the separation. They are entirely different specialties, with different objectives, and a different mindset required from those working in the field.