Ease of king touring American city (5)
I believe the answer is:
relax
'ease' is the definition.
(I've seen this before)
'king touring american city' is the wordplay.
'king' becomes 'rex' ('king' in Latin).
'touring' indicates putting letters inside (tour can mean to go around).
'american city' becomes 'LA' (Los Angeles).
'rex' enclosing 'la' is 'RELAX'.
'of' is the link.
(Other definitions for relax that I've seen before include "Loosen up, slow down" , "Slacken" , "Rest" , "Wind down" , "Become less tense" .)