Diplomacy protects royal leader returning with impetus (8)
I believe the answer is:
traction
But I can't explain it at all! Could you help me understand?
(Other definitions for traction that I've seen before include "The action of drawing or pulling over a road or track" , "Continuous pull on limb in medical treatment" , "Gripping power to permit movement" , "Use of weights and pulleys to heal a fracture" , "Which leaves on the line will affect" .)