Concentration of force with company backed by United States (5)
I believe the answer is:
focus
'concentration' is the definition.
(I know that focus is a type of concentration)
'force with company backed by united states' is the wordplay.
'force with' becomes 'f' (symbol used in Physics e.g. f=ma. I am not sure about the 'with' bit.).
'company' becomes 'co' (abbreviation).
'backed' shows that the letters should be reversed in order.
'by' says to put letters next to each other.
'united states' becomes 'US' (abbreviation for the United States).
'co' reversed gives 'oc'.
'f'+'oc'+'us'='FOCUS'
'of' is the link.
Can you help me to learn more?
(Other definitions for focus that I've seen before include "Bull's eye" , "Centre of interest or activity (5)" , "Maximum clarity of an idea" , "Concentrate, centre attention" , "Adjust camera lenses - concentrate" .)